%%% -*-BibTeX-*- %%% ==================================================================== %%% BibTeX-file{ %%% author = "Nelson H. F. Beebe", %%% version = "1.16", %%% date = "03 April 2015", %%% time = "16:37:19 MST", %%% filename = "jacm.bib", %%% address = "University of Utah %%% Department of Mathematics, 110 LCB %%% 155 S 1400 E RM 233 %%% Salt Lake City, UT 84112-0090 %%% USA", %%% telephone = "+1 801 581 5254", %%% FAX = "+1 801 581 4148", %%% checksum = "24452 9924 54454 513394", %%% email = "beebe at math.utah.edu, beebe at acm.org, %%% beebe at computer.org (Internet)", %%% codetable = "ISO/ASCII", %%% keywords = "ACM Journal of Experimental Algorithmics; %%% bibliography; BibTeX; JEA", %%% license = "public domain", %%% supported = "yes", %%% docstring = "This is a COMPLETE bibliography of the %%% ACM Journal of Experimental Algorithmics %%% (CODEN none, ISSN 1084-6654). The journal %%% appears once a year, and has no separate %%% issue numbers. %%% %%% At version 1.16, the COMPLETE year coverage %%% looked like this: %%% %%% 1996 ( 4) 2003 ( 6) 2010 ( 12) %%% 1997 ( 5) 2004 ( 6) 2011 ( 18) %%% 1998 ( 9) 2005 ( 15) 2012 ( 2) %%% 1999 ( 8) 2006 ( 17) 2013 ( 14) %%% 2000 ( 17) 2007 ( 0) 2014 ( 0) %%% 2001 ( 10) 2008 ( 29) 2015 ( 18) %%% 2002 ( 12) 2009 ( 28) %%% %%% Article: 230 %%% %%% Total entries: 230 %%% %%% The author will be grateful for reports of %%% any errors or omissions in this file; they %%% will be corrected in future editions. %%% %%% Articles and letters or corrections that %%% comment on them are cross-referenced in both %%% directions, so that citation of one of them %%% will automatically include the others. %%% %%% The ACM maintains Web pages for this journal at %%% %%% http://portal.acm.org/browse_dl.cfm?idx=J430 %%% %%% That data has been automatically converted %%% to BibTeX form, corrected for spelling and %%% page number errors, and merged into this %%% file. %%% %%% ACM copyrights explicitly permit abstracting %%% with credit, so article abstracts, keywords, %%% and subject classifications have been %%% included in this bibliography wherever %%% available. Article reviews have been %%% omitted, until their copyright status has %%% been clarified. %%% %%% Spelling has been verified with the UNIX %%% spell and GNU ispell programs using the %%% exception dictionary stored in the companion %%% file with extension .sok. %%% %%% BibTeX citation tags are uniformly chosen %%% as name:year:abbrev, where name is the %%% family name of the first author or editor, %%% year is a 4-digit number, and abbrev is a %%% 3-letter condensation of important title %%% words. Citation tags were automatically %%% generated by the biblabel software %%% developed for the BibNet Project. %%% %%% In this bibliography, entries are sorted in %%% publication order, with the help of %%% ``bibsort -byvolume''. The bibsort utility, %%% and several related programs for %%% bibliography maintenance, is available on %%% ftp.math.utah.edu in /pub/tex/bib, and at %%% other Internet sites which mirror it, %%% including the Comprehensive TeX Archive %%% Network (CTAN); the command `finger %%% ctan<at>tug.org' will produce a list of %%% CTAN hosts. %%% %%% The checksum field above contains a CRC-16 %%% checksum as the first value, followed by the %%% equivalent of the standard UNIX wc (word %%% count) utility output of lines, words, and %%% characters. This is produced by Robert %%% Solovay's checksum utility.", %%% } %%% ==================================================================== @Preamble{ "\input path.sty" # "\hyphenation{ }" # "\ifx \undefined \mathbb \def \mathbb #1{{\bf #1}}\fi" } %%% ==================================================================== %%% Acknowledgement abbreviations: @String{ack-nhfb= "Nelson H. F. Beebe, University of Utah, Department of Mathematics, 110 LCB, 155 S 1400 E RM 233, Salt Lake City, UT 84112-0090, USA, Tel: +1 801 581 5254, FAX: +1 801 581 4148, e-mail: \path|beebe@math.utah.edu|, \path|beebe@acm.org|, \path|beebe@computer.org| (Internet), URL: \path|http://www.math.utah.edu/~beebe/|"} %%% ==================================================================== %%% Journal abbreviations: @String{j-ACM-J-EXP-ALGORITHMICS= "ACM Journal of Experimental Algorithmics"} %%% ==================================================================== %%% Bibliography entries, sorted in publication order. @Article{Knuth:1996:II, author = "Donald E. Knuth", title = "Irredundant intervals", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "1", pages = "1:1--1:??", month = "????", year = "1996", CODEN = "????", DOI = "http://doi.acm.org/10.1145/235141.235146", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:01:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "This expository note presents simplifications of a theorem due to Gy{\H{o}}ri and an algorithm due to Franzblau and Kleitman: Given a family $F$ of $m$ intervals on a linearly ordered set of n elements, we can construct in $O(m + n)^2$ steps an irredundant subfamily having maximum cardinality, as well as a generating family having minimum cardinality. The algorithm is of special interest because it solves a problem analogous to finding a maximum independent set, but on a class of objects that is more general than a matroid. This note is also a complete, runnable computer program, which can be used for experiments in conjunction with the public-domain software of The Stanford GraphBase.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Gittleman:1996:PSS, author = "Arthur Gittleman", title = "Predicting string search speed", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "1", pages = "2:1--2:??", month = "????", year = "1996", CODEN = "????", DOI = "http://doi.acm.org/10.1145/235141.235147", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:01:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "String search is fundamental in many text processing applications. Sunday recently gave several algorithms to find the first occurrence of a pattern string as a substring of a text, providing experimental data from searches in a text of about 200K characters to support his claim that his algorithms are faster than the standard Boyer--Moore algorithm. We present a methodology for the average-case analysis of the performance of string search algorithms---for such algorithms, a worst-case analysis does not yield much useful information, since the performance of the algorithm is directly affected by such characteristics as the size of the character set, the character frequencies, and the structure of the text. Knuth described a finite automaton which can be used to save information about character comparisons. Baeza-Yates, Gonnet, and Regnier gave a probabilistic analysis of the worst- and average-case behavior of a string search algorithm based upon such an automaton. We construct Knuth automata to model Sunday's algorithms and use the methods of Baeza-Yates et al. to obtain an average-case analysis which confirms Sunday's experimental data.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Bader:1996:PPA, author = "David A. Bader and David R. Helman and Joseph J{\'a}J{\'a}", title = "Practical parallel algorithms for personalized communication and integer sorting", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "1", pages = "3:1--3:??", month = "????", year = "1996", CODEN = "????", DOI = "http://doi.acm.org/10.1145/235141.235148", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:01:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A fundamental challenge for parallel computing is to obtain high-level, architecture independent, algorithms which efficiently execute on general-purpose parallel machines. With the emergence of message passing standards such as MPI, it has become easier to design efficient and portable parallel algorithms by making use of these communication primitives. While existing primitives allow an assortment of collective communication routines, they do not handle an important communication event when most or all processors have non-uniformly sized personalized messages to exchange with each other. We focus in this paper on the h-relation personalized communication whose efficient implementation will allow high performance implementations of a large class of algorithms. While most previous h-relation algorithms use randomization, this paper presents a new deterministic approach for h-relation personalized communication with asymptotically optimal complexity for h>p$^2$. As an application, we present an efficient algorithm for stable integer sorting. The algorithms presented in this paper have been coded in Split-C and run on a variety of platforms, including the Thinking Machines CM-5, IBM SP-1 and SP-2, Cray Research T3D, Meiko Scientific CS-2, and the Intel Paragon. Our experimental results are consistent with the theoretical analysis and illustrate the scalability and efficiency of our algorithms across different platforms. In fact, they seem to outperform all similar algorithms known to the authors on these platforms.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{LaMarca:1996:ICP, author = "Anthony LaMarca and Richard Ladner", title = "The influence of caches on the performance of heaps", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "1", pages = "4:1--4:??", month = "????", year = "1996", CODEN = "????", DOI = "http://doi.acm.org/10.1145/235141.235145", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:01:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "As memory access times grow larger relative to processor cycle times, the cache performance of algorithms has an increasingly large impact on overall performance. Unfortunately, most commonly used algorithms were not designed with cache performance in mind. This paper investigates the cache performance of implicit heaps. We present optimizations which significantly reduce the cache misses that heaps incur and improve their overall performance. We present an analytical model called collective analysis that allows cache performance to be predicted as a function of both cache configuration and algorithm configuration. As part of our investigation, we perform an approximate analysis of the cache performance of both traditional heaps and our improved heaps in our model. In addition empirical data is given for five architectures to show the impact our optimizations have on overall performance. We also revisit a priority queue study originally performed by Jones [25]. Due to the increases in cache miss penalties, the relative performance results we obtain on today's machines differ greatly from the machines of only ten years ago. We compare the performance of implicit heaps, skew heaps and splay trees and discuss the difference between our results and Jones's.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Buchsbaum:1997:AAS, author = "Adam L. Buchsbaum and Raffaele Giancarlo", title = "Algorithmic aspects in speech recognition: an introduction", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "2", pages = "1:1--1:??", month = "????", year = "1997", CODEN = "????", DOI = "http://doi.acm.org/10.1145/264216.264219", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:14 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Speech recognition is an area with a considerable literature, but there is little discussion of the topic within the computer science algorithms literature. Many computer scientists, however, are interested in the computational problems of speech recognition. This paper presents the field of speech recognition and describes some of its major open problems from an algorithmic viewpoint. Our goal is to stimulate the interest of algorithm designers and experimenters to investigate the algorithmic problems of effective automatic speech recognition.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "automata theory; graph searching", } @Article{Battiti:1997:RSH, author = "Roberto Battiti and Marco Protasi", title = "Reactive search, a history-sensitive heuristic for {MAX}-{SAT}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "2", pages = "2:1--2:??", month = "????", year = "1997", CODEN = "????", DOI = "http://doi.acm.org/10.1145/264216.264220", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:14 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The Reactive Search (RS) method proposes the integration of a simple history-sensitive (machine learning) scheme into local search for the on-line determination of free parameters. In this paper a new RS algorithm is proposed for the approximated solution of the Maximum Satisfiability problem: a component based on local search with temporary prohibitions (Tabu Search) is complemented with a reactive scheme that determines the appropriate value of the prohibition parameter by monitoring the Hamming distance along the search trajectory. The proposed algorithm (H-RTS) can therefore be characterized as a dynamic version of Tabu Search. In addition, the non-oblivious functions recently introduced in the framework of approximation algorithms are used to discover a better local optimum in the initial part of the search. The algorithm is developed in two phases. First the bias-diversification properties of individual candidate components are analyzed by extensive empirical evaluation, then a reactive scheme is added to the winning component, based on Tabu Search. The final tests on a benchmark of random MAX-3-SAT and MAX-4-SAT problems demonstrate the superiority of H-RTS with respect to alternative heuristics.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Smith:1997:EHF, author = "Bradley J. Smith and Gregory L. Heileman and Chaouki Abdallah", title = "The exponential hash function", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "2", pages = "3:1--3:??", month = "????", year = "1997", CODEN = "????", DOI = "http://doi.acm.org/10.1145/264216.264221", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:14 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper an efficient open address hash function called exponential hashing is developed. The motivation for this hash function resulted from our ongoing efforts to apply dynamical systems theory to the study of hashing; however, the analysis conducted in this paper is primarily based on traditional number theory. Proofs of optimal table parameter choices are provided for a number of hash functions. We also demonstrate experimentally that exponential hashing essentially matches the performance of a widely-used optimal double hash function for uniform data distributions, and performs significantly better for nonuniform data distributions. We show that exponential hashing exhibits a higher integer Lyapunov exponent and entropy than double hashing for initial data probes, which offers one explanation for its improved performance on nonuniform data distributions.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "ADT; chaos; dynamic dictionary; dynamical systems theory; exponential hashing; Lyapunov exponent; number theory", } @Article{Purchase:1997:ESB, author = "H. C. Purchase and R. F. Cohen and M. I. James", title = "An experimental study of the basis for graph drawing algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "2", pages = "4:1--4:??", month = "????", year = "1997", CODEN = "????", DOI = "http://doi.acm.org/10.1145/264216.264222", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:14 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Designers of graph drawing algorithms and systems claim to illuminate application data by producing layouts that optimise measurable aesthetic qualities. Examples of these aesthetics include symmetry (where possible, a symmetrical view of the graph should be displayed), minimise arc crossing(the number of arc crossings in the display should be minimised), and minimise bends (the total number of bends in polyline arcs should be minimised).The aim of this paper is to describe our work to validate these claims by performing empirical studies of human understanding of graphs drawn using various layout aesthetics. This work is important since it helps indicate to algorithm and system designers what are the aesthetic qualities most important to aid understanding, and consequently to build more effective systems.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "human-computer interaction", } @Article{Alberts:1997:ESD, author = "David Alberts and Giuseppe Cattaneo and Giuseppe F. Italiano", title = "An empirical study of dynamic graph algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "2", pages = "5:1--5:??", month = "????", year = "1997", CODEN = "????", DOI = "http://doi.acm.org/10.1145/264216.264223", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:14 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The contributions of this paper are both of theoretical and of experimental nature. From the experimental point of view, we conduct an empirical study on some dynamic connectivity algorithms which where developed recently. In particular, the following implementations were tested and compared with simple algorithms: simple sparsification by Eppstein et al. and the recent randomized algorithm by Henzinger and King. In our experiments, we considered both random and non-random inputs. Moreover, we present a simplified variant of the algorithm by Henzinger and King, which for random inputs was always faster than the original implementation. For non-random inputs, simple sparsification was the fastest algorithm for small sequences of updates; for medium and large sequences of updates, the original algorithm by Henzinger and King was faster. From the theoretical point of view, we analyze the average case running time of simple sparsification and prove that for dynamic random graphs its logarithmic overhead vanishes.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Hemaspaandra:1998:PBA, author = "Lane A. Hemaspaandra and Kulathur S. Rajasethupathy and Prasanna Sethupathy and Marius Zimand", title = "Power balance and apportionment algorithms for the {United States Congress}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "1:1--1:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297106", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We measure the performance, in the task of apportioning the Congress of the United States, of an algorithm combining a heuristic-driven (simulated annealing) search with an exact-computation dynamic programming evaluation of the apportionments visited in the search. We compare this with the actual algorithm currently used in the United States to apportion Congress, and with a number of other algorithms that have been proposed. We conclude that on every set of census data in this country's history, the heuristic-driven apportionment provably yields far fairer apportionments than those of any of the other algorithm considered, including the algorithm currently used by the United States for Congressional apportionment.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "apportionment algorithms; power indices; simulated annealing", } @Article{Cho:1998:WBL, author = "Seonghun Cho and Sartaj Sahni", title = "Weight-biased leftist trees and modified skip lists", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "2:1--2:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297111", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We propose the weight biased leftist tree as an alternative to traditional leftist trees [CRAN72] for the representation of mergeable priority queues. A modified version of skip lists [PUGH90] that uses fixed size nodes is also proposed. Experimental results show our modified skip list structure is faster than the original skip list structure for the representation of dictionaries. Experimental results comparing weight biased leftist trees and competing priority queue structures are presented.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dictionary; leftist trees; priority queues; skip lists", } @Article{Yan:1998:LBE, author = "Yong Yan and Xiaodong Zhang", title = "Lock bypassing: an efficient algorithm for concurrently accessing priority heaps", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "3:1--3:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297116", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The heap representation of priority queues is one of the most widely used data structures in the design of parallel algorithms. Efficiently exploiting the parallelism of a priority heap has significant influence on the efficiency of a wide range of applications and parallel algorithms. In this paper, we propose an aggressive priority heap operating algorithm, called the lock bypassing algorithm (LB) on shared memory systems. This algorithm minimizes interference of concurrent enqueue and dequeue operations on priority heaps while keeping the strict priority property: a dequeue always returns the minimum of a heap. The unique idea that distinguishes the LB algorithm from previous concurrent algorithms on priority heaps is the use of locking-on-demand and lock-bypassing techniques to minimize locking granularity and to maximize parallelism. The LB algorithm allows an enqueue operation to bypass the locks along its insertion path until it reaches a possible place where it can perform the insertion. Meanwhile a dequeue operation also makes its locking range and locking period as small as possible by carefully tuning its execution procedure. The LB algorithm is shown to be correct in terms of deadlock freedom and heap consistency. The performance of the LB algorithm was evaluated analytically and experimentally in comparison with previous algorithms. Analytical results show that the LB algorithm reduces by half the number of locks waited for in the worst case by previous algorithms. The experimental results show that the LB algorithm outperforms previously designed algorithms by up to a factor of 2 in hold time.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "aggressive locking; parallel algorithm; performance evaluation; priority heap; shared-memory system", } @Article{Helman:1998:NDP, author = "David R. Helman and Joseph J{\'a}J{\'a} and David A. Bader", title = "A new deterministic parallel sorting algorithm with an experimental evaluation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "4:1--4:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297128", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We introduce a new deterministic parallel sorting algorithm for distributed memory machines based on the regular sampling approach. The algorithm uses only two rounds of regular all-to-all personalized communication in a scheme that yields very good load balancing with virtually no overhead. Moreover, unlike previous variations, our algorithm efficiently handles the presence of duplicate values without the overhead of tagging each element with a unique identifier. This algorithm was implemented in SPLIT-C and run on a variety of platforms, including the Thinking Machines CM-5, the IBM SP-2-WN, and the Cray Research T3D. We ran our code using widely different benchmarks to examine the dependence of our algorithm on the input distribution. Our experimental results illustrate the efficiency and scalability of our algorithm across different platforms. In fact, the performance compares closely to that of our random sample sort algorithm, which seems to outperform all similar algorithms known to the authors on these platforms. Together, their performance is nearly invariant over the set of input distributions, unlike previous efficient algorithms. However, unlike our randomized sorting algorithm, the performance and memory requirements of our regular sorting algorithm can be deterministically guaranteed.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "generalized sorting; integer sorting; parallel algorithms; parallel performance; sorting by regular sampling", } @Article{Frigioni:1998:EAD, author = "Daniele Frigioni and Mario Ioffreda and Umberto Nanni and Giulio Pasqualone", title = "Experimental analysis of dynamic algorithms for the single", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "5:1--5:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297147", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper we propose the first experimental study of the fully dynamic single-source shortest-paths problem on directed graphs with positive real edge weights. In particular, we perform an experimental analysis of three different algorithms: Dijkstra's algorithm, and the two output bounded algorithms proposed by Ramalingam and Reps in [30] and by Frigioni, Marchetti-Spaccamela and Nanni in [18], respectively. The main goal of this paper is to provide a first experimental evidence for: (a) the effectiveness of dynamic algorithms for shortest paths with respect to a traditional static approach to this problem; (b) the validity of the theoretical model of output boundedness to analyze dynamic graph algorithms. Beside random generated graphs, useful to capture the 'asymptotic' behavior of the algorithms, we also developed experiments by considering a widely used graph from the real world, i.e., the Internet graph.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dynamic algorithms; experimental analysis of algorithms; shortest paths", } @Article{Magun:1998:GMA, author = "Jakob Magun", title = "Greeding matching algorithms, an experimental study", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "6:1--6:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297131", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We conduct an experimental study of several greedy algorithms for finding large matchings in graphs. Further we propose a new graph reduction, called $k$-Block Reduction, and present two novel algorithms using extra heuristics in the matching step and $k$-Block Reduction for $k = 3$. Greedy matching algorithms can be used for finding a good approximation of the maximum matching in a graph $G$ if no exact solution is required, or as a fast preprocessing step to some other matching algorithm. The studied greedy algorithms run in $O(m)$. They are easy to implement and their correctness and their running time are simple to prove. Our experiments show that a good greedy algorithm looses on average at most one edge on random graphs from $G(n,p)$ with up to 10,000 vertices. Furthermore the experiments show for which edge densities in random graphs the maximum matching problem is difficult to solve.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Andersson:1998:IR, author = "Arne Andersson and Stefan Nilsson", title = "Implementing radixsort", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "7:1--7:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297136", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present and evaluate several optimization and implementation techniques for string sorting. In particular, we study a recently published radix sorting algorithm, Forward radixsort, that has a provably good worst-case behavior. Our experimental results indicate that radix sorting is considerably faster (often more than twice as fast) than comparison-based sorting methods. This is true even for small input sequences. We also show that it is possible to implement a radixsort with good worst-case running time without sacrificing average-case performance. Our implementations are competitive with the best previously published string sorting programs.", acknowledgement = ack-nhfb, articleno = "7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "adaptive radixsort; algorithms; forward radixsort; radix sorting; sorting; string sorting", } @Article{Cherkassky:1998:APC, author = "Boris V. Cherkassky and Andrew V. Goldberg and Paul Martin and Joao C. Setubal and Jorge Stolfi", title = "Augment or push: a computational study of bipartite matching and unit-capacity flow algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "8:1--8:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297140", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We conduct a computational study of unit capacity flow and bipartite matching algorithms. Our goal is to determine which variant of the push-relabel method is most efficient in practice and to compare push-relabel algorithms with augmenting path algorithms. We have implemented and compared three push-relabel algorithms, three augmenting-path algorithms (one of which is new), and one augment-relabel algorithm. The depth-first search augmenting path algorithm was thought to be a good choice for the bipartite matching problem, but our study shows that it is not robust (meaning that it is not consistently fast on all or most inputs). For the problems we study, our implementations of the FIFO and lowest-level selection push-relabel algorithms have the most robust asymptotic rate of growth and work best overall. Augmenting path algorithms, although not as robust, on some problem classes are faster by a moderate constant factor. Our study includes several new problem families and input graphs with as many as $5 \times 105$ vertices.", acknowledgement = ack-nhfb, articleno = "8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Radzik:1998:IDT, author = "Tomasz Radzik", title = "Implementation of dynamic trees with in-subtree operations", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "3", pages = "9:1--9:??", month = "????", year = "1998", CODEN = "????", DOI = "http://doi.acm.org/10.1145/297096.297144", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We describe an implementation of dynamic trees with 'in-subtree' operations. Our implementation follows Sleator and Tarjan's framework of dynamic-tree implementations based on splay trees. We consider the following two examples of 'in-subtree' operations. (a) For a given node v, find a node with the minimum key in the subtree rooted at v. (b) For a given node v, find a random node with key X in the subtree rooted at v (value X is fixed throughout the whole computation). The first operation may provide support for edge deletions in the dynamic minimum spanning tree problem. The second one may be useful in local search methods for degree-constrained minimum spanning tree problems. We conducted experiments with our dynamic-tree implementation within these two contexts, and the results suggest that this implementation may lead to considerably faster codes than straightforward approaches do.", acknowledgement = ack-nhfb, articleno = "9", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; design; dynamic minimum spanning tree; dynamic trees; experimentation; performance; splay trees", } @Article{Burke:1999:MAS, author = "E. K. Burke and A. J. Smith", title = "A memetic algorithm to schedule planned maintenance for the national grid", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "1:1--1:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347801", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The combination of local search operators, problem specific information and a genetic algorithm has provided very good results in certain scheduling problems, particularly in timetabling and maintenance scheduling problems. The resulting algorithm from this hybrid approach has been termed a Memetic Algorithm. This paper investigates the use of such an algorithm for the scheduling of transmission line maintenance for a known problem that has been addressed in the literature using a combination of a genetic algorithm and greedy optimisers. This problem is concerned with the scheduling of maintenance for an electricity transmission network where every transmission line must be maintained once within a specified time period. The objective is to avoid situations where sections of the network are disconnected, and to minimise the overloading of lines which are in service. In this paper we look at scheduling maintenance for the South Wales region of the national transmission network. We present and discuss, in some detail, a memetic algorithm that incorporates local search operators including tabu search and simulated annealing. A comparison is made both with the results from previous work, and against a selection of optimising techniques. The approach presented in this paper shows a significant improvement over previously published results on previously tackled problems. We also present results on another problem which has not been tackled in the literature but which is closer to the real world maintenance scheduling problems faced by such companies as The National Grid Company plc using the South Wales region.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "heuristics; hill climbing; maintenance scheduling; memetic algorithms; simulated annealing; tabu search", } @Article{Kim:1999:NSP, author = "Sun Kim", title = "A new string-pattern matching algorithm using partitioning and hashing efficiently", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "2:1--2:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347803", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper, we present a new string-pattern matching algorithm that partitions the text into segments of the input pattern length and searches for pattern occurrences using a simple hashing scheme. Unlike the well known Boyer--Moore style algorithm, our algorithm does not compute variable shift length, thus providing a conceptually simpler way to search for patterns. Empirical evaluation shows that our algorithm runs significantly faster than Sunday's and Horspool's extensions of the Boyer--Moore algorithm. The notion of the non-occurrence heuristic used in our algorithm, together with a text partitioning scheme, leads to a simplified scheme for searching for pattern occurrences, thus yielding better run time performance.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Eiron:1999:MMC, author = "N. Eiron and M. Rodeh and I. Steinwarts", title = "Matrix multiplication: a case study of enhanced data cache utilization", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "3:1--3:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347806", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Modern machines present two challenges to algorithm engineers and compiler writers: They have superscalar, super-pipelined structure, and they have elaborate memory subsystems specifically designed to reduce latency and increase bandwidth. Matrix multiplication is a classical benchmark for experimenting with techniques used to exploit machine architecture and to overcome the limitations of contemporary memory subsystems. This research aims at advancing the state of the art of algorithm engineering by balancing instruction level parallelism, two levels of data tiling, copying to provably avoid any cache conflicts, and prefetching in parallel to computational operations, in order to fully exploit the memory bandwidth. Measurements on IBM's RS/6000 43P workstation show that the resultant matrix multiplication algorithm outperforms IBM's ESSL by 6.8-31.8\%, is less sensitive to the size of the input data, and scales better. In this paper we introduce a cache aware algorithm for matrix multiplication. We also suggest generic guidelines that may be applied to compute intensive algorithm to efficiently utilize the data cache. We believe that some of our concepts may be embodied in compilers.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; BLAS; blocking; cache; matrix multiplication; performance; prefetching", } @Article{Erlebach:1999:EIO, author = "T. Erlebach and K. Jansen", title = "Efficient implementation of an optimal greedy algorithm for wavelength assignment in directed tree networks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "4:1--4:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347808", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In all-optical networks with wavelength-division multiplexing several connections can share a physical link if the signals are transmitted on different wavelengths. As the number of available wavelengths is limited in practice, it is important to find wavelength assignments minimizing the number of different wavelengths used. This path coloring problem is NP-hard, and the best known polynomial-time approximation algorithm for directed tree networks achieves approximation ratio $5 / 3$, which is optimal in the class of greedy algorithms for this problem. It is shown how the algorithm can be modified in order to improve its running-time to $O({\rm Tec}(N,L))$ for sets of paths with maximum load $L$ in trees with $N$ nodes, where ${\rm Tec}(n, k)$ is the time for edge-coloring a $k$-regular bipartite graph with n nodes. An implementation of this efficient version of the algorithm in C++ using the LEDA class library is described, and experimental results regarding the running-times and the number of wavelengths used are reported. An additional heuristic that reduces the number of wavelengths used in the average case while maintaining the worst-case bound of $5 L / 3$ is described.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; bipartite edge coloring; directed tree networks; experimentation; path coloring", } @Article{Huson:1999:HTR, author = "D. Huson and S. Nettles and K. Rice and T. Warnow and S. Yooseph", title = "Hybrid tree reconstruction methods", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "5:1--5:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347812", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A major computational problem in biology is the reconstruction of evolutionary trees for species sets, and accuracy is measured by comparing the topologies of the reconstructed tree and the model tree. One of the major debates in the field is whether large evolutionary trees can be even approximately accurately reconstructed from biomolecular sequences of realistically bounded lengths (up to about 2000 nucleotides) using standard techniques (polynomial-time distance methods, and heuristics for NP-hard optimization problems). Using both analytical and experimental techniques, we show that on large trees, the two most popular methods in systematic biology, Neighbor-Joining and Maximum Parsimony heuristics, as well as two promising methods introduced by theoretical computer scientists, are all likely to have significant errors in the topology reconstruction of the model tree. We also present a new general technique for combining outputs of different methods (thus producing hybrid methods), and show experimentally how one such hybrid method has better performance than its constituent parts.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Jacob:1999:CSR, author = "R. Jacob and M. Marathe and K. Nagel", title = "A computational study of routing algorithms for realistic transportation networks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "6:1--6:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347814", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We carry out an experimental analysis of a number of shortest-path (routing) algorithms investigated in the context of the TRANSIMS (TRansportation ANalysis and SIMulation System) project. The main focus of the paper is to study how various heuristic as well as exact solutions and associated data structures affect the computational performance of the software developed for realistic transportation networks. For this purpose we have used a road network representing, with high degree of resolution, the Dallas Fort-Worth urban area. We discuss and experimentally analyze various one-to-one shortest-path algorithms. These include classical exact algorithms studied in the literature as well as heuristic solutions that are designed to take into account the geometric structure of the input instances. Computational results are provided to compare empirically the efficiency of various algorithms. Our studies indicate that a modified Dijkstra's algorithm is computationally fast and an excellent candidate for use in various transportation planning applications as well as ITS related technologies.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "design and analysis of algorithms; experimental analysis; network design; shortest-paths algorithms; transportation planning", } @Article{Muller-Hannemann:1999:IWM, author = "M. M{\"u}ller-Hannemann and A. Schwartz", title = "Implementing weighted $b$-matching algorithms: towards a flexible software design", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "7:1--7:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347815", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present a case study on the design of an implementation of a fundamental combinatorial optimization problem: weighted b-matching. Although this problem is well-understood in theory and efficient algorithms are known, only little experience with implementations is available. This study was motivated by the practical need for an efficient b-matching solver as a subroutine in our approach to a mesh refinement problem in computer-aided design (CAD).The intent of this paper is to demonstrate the importance of flexibility and adaptability in the design of complex algorithms, but also to discuss how such goals can be achieved for matching algorithms by the use of design patterns. Starting from the basis of the famous blossom algorithm we explain how to exploit in different ways the flexibility of our software design which allows an incremental improvement of efficiency by exchanging subalgorithms and data structures. In a comparison with a code by Miller and Pekny we also demonstrate that our implementation is even without fine-tuning very competitive. Our code is significantly faster, with improvement factors ranging between 15 and 466 on TSPLIB instances.", acknowledgement = ack-nhfb, articleno = "7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; b-matching; blossom algorithm; design patterns; experimentation; object-oriented design; software design", } @Article{Schwerdt:1999:CWT, author = "J. Schwerdt and M. Smid and J. Majhi and R. Janardan", title = "Computing the width of a three-dimensional point set: an experimental study", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "4", pages = "8:1--8:??", month = "????", year = "1999", CODEN = "????", DOI = "http://doi.acm.org/10.1145/347792.347816", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:02:52 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We describe a robust, exact, and efficient implementation of an algorithm that computes the width of a three-dimensional point set. The algorithm is based on efficient solutions to problems that are at the heart of computational geometry: three-dimensional convex hulls, point location in planar graphs, and computing intersections between line segments. The latter two problems have to be solved for planar graphs and segments on the unit sphere, rather than in the two-dimensional plane. The implementation is based on LEDA, and the geometric objects are represented using exact rational arithmetic.", acknowledgement = ack-nhfb, articleno = "8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "computational geometry; implementation; layered manufacturing; spherical geometry", } @Article{Eppstein:2000:FHC, author = "David Eppstein", title = "Fast hierarchical clustering and other applications of dynamic closest pairs", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "1:1--1:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.351829", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We develop data structures for dynamic closest pair problems with arbitrary distance functions, that do not necessarily come from any geometric structure on the objects. Based on a technique previously used by the author for Euclidean closest pairs, we show how to insert and delete objects from an n-object set, maintaining the closest pair, in $O(n \log^2 n)$ time per update and $O(n)$ space. With quadratic space, we can instead use a quadtree-like structure to achieve an optimal time bound, $O(n)$ per update. We apply these data structures to hierarchical clustering, greedy matching, and TSP heuristics, and discuss other potential applications in machine learning, Gr{\"o}bner bases, and local improvement algorithms for partition and placement problems. Experiments show our new methods to be faster in practice than previously used heuristics.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "conga line data structure; matching; nearest-neighbor heuristic; quadtree; TSP", } @Article{Chong:2000:CBD, author = "Kyn-Rak Chong and Sartaj Sahni", title = "Correspondence-based data structures for double-ended priority queues", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "2:1--2:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.351828", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We describe three general methods--total, dual, and leaf correspondence--that may be used to derive efficient double-ended priority queues from single-ended priority queues. These methods are illustrated by developing double-ended priority queues based on the classical heap. Experimental results indicate that the leaf-correspondence method generally leads to a faster double-ended priority queue than either total or dual correspondence. On randomly generated test sets, however, the splay tree outperforms the tested correspondence-based double-ended priority queues.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "correspondence-based data structures; double-ended priority queues; heaps; leftist trees; runtime efficiency; splay trees", } @Article{Xiao:2000:IMP, author = "Li Xiao and Xiaodong Zhang and Stefan A. Kubricht", title = "Improving memory performance of sorting algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "3:1--3:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384245", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Memory hierarchy considerations during sorting algorithm design and implementation play an important role in significantly improving execution performance. Existing algorithms mainly attempt to reduce capacity misses on direct-mapped caches. To reduce other types of cache misses that occur in the more common set-associative caches and the TLB, we restructure the mergesort and quicksort algorithms further by integrating tiling, padding, and buffering techniques and by repartitioning the data set. Our study shows that substantial performance improvements can be obtained using our new methods.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "caches; memory performance; mergesort; quicksort; TLB", } @Article{Navarro:2000:FFS, author = "Gonzalo Navarro and Mathieu Raffinot", title = "Fast and flexible string matching by combining bit-parallelism and suffix automata", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "4:1--4:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384246", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The most important features of a string matching algorithm are its efficiency and its flexibility. Efficiency has traditionally received more attention, while flexibility in the search pattern is becoming a more and more important issue. Most classical string matching algorithms are aimed at quickly finding an exact pattern in a text, being Knuth--Morris--Pratt (KMP) and the Boyer--Moore (BM) family the most famous ones. A recent development uses deterministic 'suffix automata' to design new optimal string matching algorithms, e.g. BDM and TurboBDM. Flexibility has been addressed quite separately by the use of 'bit-parallelism', which simulates automata in their nondeterministic form by using bits and exploiting the intrinsic parallelism inside the computer word, e.g. the Shift-Or algorithm. Those algorithms are extended to handle classes of characters and errors in the pattern and/or in the text, their drawback being their inability to skip text characters. In this paper we merge bit-parallelism and suffix automata, so that a nondeterministic suffix automaton is simulated using bit-parallelism. The resulting algorithm, called BNDM, obtains the best from both worlds. It is much simpler to implement than BDM and nearly as simple as Shift-Or. It inherits from Shift-Or the ability to handle flexible patterns and from BDM the ability to skip characters. BNDM is 30\%-40\% faster than BDM and up to 7 times faster than Shift-Or. When compared to the fastest existing algorithms on exact patterns (which belong to the BM family), BNDM is from 20\% slower to 3 times faster, depending on the alphabet size. With respect to flexible pattern searching, BNDM is by far the fastest technique to deal with classes of characters and is competitive to search allowing errors. In particular, BNDM seems very adequate for computational biology applications, since it is the fastest algorithm to search on DNA sequences and flexible searching is an important problem in that area. As a theoretical development related to flexible pattern matching, we introduce a new automaton to recognize suffixes of patterns with classes of characters. To the best of our knowledge, this automaton has not been studied before.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Caldwell:2000:DIM, author = "Andrew E. Caldwell and Andrew B. Kahng and Igor L. Markov", title = "Design and implementation of move-based heuristics for {VLSI} hypergraph partitioning", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "5:1--5:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384247", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We summarize the techniques of implementing move-based hypergraph partitioning heuristics and evaluating their performance in the context of VLSI design applications. Our first contribution is a detailed software architecture, consisting of seven reusable components, that allows flexible, efficient and accurate assessment of the practical implications of new move-based algorithms and partitioning formulations. Our second contribution is an assessment of the modern context for hypergraph partitioning research for VLSI design applications. In particular, we discuss the current level of sophistication in implementation know-how and experimental evaluation, and we note how requirements for real-world partitioners --- if used as motivation for research --- should affect the evaluation of prospective contributions. Two 'implicit decisions' in the implementation of the Fiduccia-Mattheyses heuristic are used to illustrate the difficulty of achieving meaningful experimental evaluation of new algorithmic ideas.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; balanced min-cut hypergraph partitioning; experimentation; measurement; performance; VLSI CAD", } @Article{Levine:2000:FRC, author = "Matthew S. Levine", title = "Finding the right cutting planes for the {TSP}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "6:1--6:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384248", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Given an instance of the Traveling Salesman Problem (TSP), a reasonable way to get a lower bound on the optimal answer is to solve a linear programming relaxation of an integer programming formulation of the problem. These linear programs typically have an exponential number of constraints, but in theory they can be solved efficiently with the ellipsoid method as long as we have an algorithm that can take a solution and either declare it feasible or find a violated constraint. In practice, it is often the case that many constraints are violated, which raises the question of how to choose among them so as to improve performance. For the simplest TSP formulation it is possible to efficiently find all the violated constraints, which gives us a good chance to try to answer this question empirically. Looking at random two dimensional Euclidean instances and the large instances from TSPLIB, we ran experiments to evaluate several strategies for picking among the violated constraints. We found some information about which constraints to prefer, which resulted in modest gains, but were unable to get large improvements in performance.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; combinatorial optimization; cutting plane; experimentation; minimum cut; performance; traveling salesman problem", } @Article{Sanders:2000:FPQ, author = "Peter Sanders", title = "Fast priority queues for cached memory", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "7:1--7:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384249", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The cache hierarchy prevalent in todays high performance processors has to be taken into account in order to design algorithms that perform well in practice. This paper advocates the adaption of external memory algorithms to this purpose. This idea and the practical issues involved are exemplified by engineering a fast priority queue suited to external memory and cached memory that is based on k-way merging. It improves previous external memory algorithms by constant factors crucial for transferring it to cached memory. Running in the cache hierarchy of a workstation the algorithm is at least two times faster than an optimized implementation of binary heaps and 4-ary heaps for large inputs.", acknowledgement = ack-nhfb, articleno = "7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "cache; cache efficiency; data structure; external memory; heap; implementation; multi way merging; priority queue; secondary storage", } @Article{Muller-Hannemann:2000:IWM, author = "Matthias M{\"u}ller-Hannemann and Alexander Schwartz", title = "Implementing weighted $b$-matching algorithms: insights from a computational study", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "8:1--8:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384250", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present an experimental study of an implementation of weighted perfect b-matching based on the primal-dual blossom algorithm. Although this problem is well-understood in theory and efficient algorithms are known, only little experience with implementations is available. In this paper several algorithmic variants are compared on synthetic and application problem data of very sparse graphs. This study was motivated by the practical need for an efficient b-matching solver for the latter application, namely as a subroutine in our approach to a mesh refinement problem in computer-aided design (CAD).Linear regression and operation counting is used to analyze code variants. The experiments confirm that a fractional jump-start speeds up the algorithm, they indicate that a variant based on pairing heaps is slightly superior to a k-heap variant, and that scaling of large b-values is not necessary, whereas a delayed blossom shrinking heuristic significantly improves running times only for graphs with average degree two. The fastest variant of our implementation appears to be highly superior to a code by Miller and Pekny (1995).", acknowledgement = ack-nhfb, articleno = "8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "b-matching; blossom algorithm; operation counting", } @Article{Shibuya:2000:CSP, author = "Tetsuo Shibuya", title = "Computing the $n \times m$ shortest path efficiently", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "9:1--9:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384251", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Computation of all the shortest paths between multiple sources and multiple destinations on various networks is required in many problems, such as the traveling salesperson problem (TSP) and the vehicle routing problem (VRP). This paper proposes new algorithms that compute the set of shortest paths efficiently by using the A* algorithm. The efficiency and properties of these algorithms are examined by using the results of experiments on an actual road network.", acknowledgement = ack-nhfb, articleno = "9", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "*{$<$} m shortest paths; algorithm; algorithms; A{$<$} experimentation; GIS; n \times /sup{$>$} sup>", } @Article{Vishkin:2000:ELR, author = "Dascal Vishkin and Uzi Vishkin", title = "Experiments with list ranking for explicit multi-threaded {(XMT)} instruction parallelism", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "10:1--10:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384252", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Algorithms for the problem of list ranking are empirically studied with respect to the Explicit Multi-Threaded (XMT) platform for instruction-level parallelism (ILP). The main goal of this study is to understand the differences between XMT and more traditional parallel computing implementation platforms/models as they pertain to the well studied list ranking problem. The main two findings are: (i) good speedups for much smaller inputs are possible and (ii) in part, the first finding is based on a new variant of a 1984 algorithm, called the No-Cut algorithm. The paper incorporates analytic (non-asymptotic) performance analysis into experimental performance analysis for relatively small inputs. This provides an interesting example where experimental research and theoretical analysis complement one another. Explicit Multi-Threading (XMT) is a fine-grained computation framework introduced in our SPAA'98 paper. Building on some key ideas of parallel computing, XMT covers the spectrum from algorithms through architecture to implementation; the main implementation related innovation in XMT was through the incorporation of low-overhead hardware and software mechanisms (for more effective fine-grained parallelism). The reader is referred to that paper for detail on these mechanisms. The XMT platform aims at faster single-task completion time by way of ILP.", acknowledgement = ack-nhfb, articleno = "10", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Werneck:2000:FMC, author = "Renato Werneck and Jo{\~a}o Setubal and Arlindo da Conceic{\~a}o", title = "Finding minimum congestion spanning trees", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "11:1--11:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384253", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Given a weighted graph $G = (V, E)$, a positive integer $k$, and a penalty function $w_p$, we want to find $k$ spanning trees on $G$, not necessarily disjoint, of minimum total weight, such that the weight of each edge is subject to a penalty given by $w_p$ if it belongs to more than one tree. The objective function to be minimized is $\sum_{e \in E} W_e(i_e)$, where $i_e$ is the number of times edge $e$ appears in the solution and $W_e(i_e) = i_e w_p(e, i_e)$ is the aggregate cost of using edge $e$ $i_e$ times. For the case when $W_e$ is weakly convex, which should have wide application in congestion problems, we present a polynomial time algorithm; the algorithm's complexity is quadratic in $k$. We also present two heuristics with complexity linear in $k$. In an experimental study we show that these heuristics are much faster than the exact algorithm also in practice. These experiments present a diverse combination of input families (four), varying $k$ (up to 1000), and penalty functions (two). In most inputs tested the solutions given by the heuristics were within 1\% of optimal or much better, especially for large $k$. The worst quality observed was 3.2\% of optimal.", acknowledgement = ack-nhfb, articleno = "11", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Schulz:2000:DAL, author = "Frank Schulz and Dorothea Wagner and Karsten Weihe", title = "{Dijkstra}'s algorithm on-line: an empirical case study from public railroad transport", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "12:1--12:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384254", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Traffic information systems are among the most prominent real-world applications of Dijkstra's algorithm for shortest paths. We consider the scenario of a central information server in the realm of public railroad transport on wide-area networks. Such a system has to process a large number of on-line queries for optimal travel connections in real time. In practice, this problem is usually solved by heuristic variations of Dijkstra's algorithm, which do not guarantee an optimal result. We report results from a pilot study, in which we focused on the travel time as the only optimization criterion. In this study, various speed-up techniques for Dijkstra's algorithm were analysed empirically. This analysis was based on the timetable data of all German trains and on a 'snapshot' of half a million customer queries.", acknowledgement = ack-nhfb, articleno = "12", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Flato:2000:DIP, author = "Eyal Flato and Dan Halperin and Iddo Hanniel and Oren Nechushtan and Eti Ezra", title = "The design and implementation of planar maps in {CGAL}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "13:1--13:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384255", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Planar maps are fundamental structures in computational geometry. They are used to represent the subdivision of the plane into regions and have numerous applications. We describe the planar map package of CGAL--a Computational Geometry Algorithms Library. We discuss its modular design and implementation. In particular we introduce the two main classes of the design--planar maps and topological maps that enable the convenient separation between geometry and topology. The modular design is implemented using a generic programming approach. By switching a template parameter--the geometric traits class, one can use the same code for planar maps of different objects such as line segments or circular arcs. More flexibility is achieved by choosing a point location algorithm out of three implemented algorithms or plugging in an algorithm implemented by the user. The user of the planar maps package can benefit both from its flexibility and robustness. We present several examples of geometric traits classes and point location algorithms which demonstrate the possibility to adapt the general package to specific needs.", acknowledgement = ack-nhfb, articleno = "13", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Rahman:2000:ACE, author = "Naila Rahman and Rajeev Raman", title = "Analysing cache effects in distribution sorting", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "14:1--14:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384256", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study cache effects in distribution sorting algorithms for sorting keys drawn independently at random from a uniform distribution (`uniform keys'). We note that the performance of a recently-published distribution sorting algorithm, Flashsort1, which sorts $n$ uniform floating-point keys in $O(n)$ expected time, does not scale well with the input size due to poor cache utilisation. We present an approximate analysis for distribution sorting uniform keys which, as validated by simulation results, predicts the expected cache misses of Flashsort1 quite well. Using this analysis, we design a multiple-pass variant of Flashsort1 which outperforms Flashsort1 and comparison-based algorithms on uniform floating-point keys for moderate to large values of $n$. Using experimental results we also show that the integer distribution sorting algorithm MSB radix sort performs well on both uniform integer and uniform floating-point keys.", acknowledgement = ack-nhfb, articleno = "14", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "cache; efficient sorting algorithms; external-memory algorithms; memory hierarchy", } @Article{Bojesen:2000:PEC, author = "Jesper Bojesen and Jyrki Katajainen and Maz Spork", title = "Performance engineering case study: heap construction", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "15:1--15:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384257", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The behaviour of three methods for constructing a binary heap on a computer with a hierarchical memory is studied. The methods considered are the original one proposed by Williams [1964], in which elements are repeatedly inserted into a single heap; the improvement by Floyd [1964], in which small heaps are repeatedly merged to bigger heaps; and a recent method proposed, e.g., by Fadel et al. [1999] in which a heap is built layerwise. Both the worst-case number of instructions and that of cache misses are analysed. It is well-known that Floyd's method has the best instruction count. Let N denote the size of the heap to be constructed, B the number of elements that fit into a cache line, and let c and d be some positive constants. Our analysis shows that, under reasonable assumptions, repeated insertion and layerwise construction both incur at most cN/B cache misses, whereas repeated merging, as programmed by Floyd, can incur more than (dN log2 B)/B cache misses. However, for our memory-tuned versions of repeated insertion and repeated merging the number of cache misses incurred is close to the optimal bound N/B. In addition to these theoretical findings, we communicate many practical experiences which we hope to be valuable for others doing experimental algorithmic work.", acknowledgement = ack-nhfb, articleno = "15", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; binary heaps; code tuning; experimentation; memory tuning; performance; theory", } @Article{Boghossian:2000:RSP, author = "N. P. Boghossian and O. Kohlbacher and H. P. Lenhof", title = "Rapid software prototyping in molecular modeling using the biochemical algorithms library {(BALL)}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "16:1--16:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384258", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In the next century, virtual laboratories will play a key role in biotechnology. Computer experiments will not only replace some of the time-consuming and expensive real-world experiments, but they will also provide insights that cannot be obtained using 'wet' experiments. The field that deals with the modeling of atoms, molecules, and their reactions is called Molecular Modeling. The advent of Life Sciences gave rise to numerous new developments in this area. However, the implementation of new simulation tools is extremely time-consuming. This is mainly due to the large amount of supporting code that is required in addition to the code necessary to implement the new idea. The only way to reduce the development time is to reuse reliable code, preferably using object-oriented approaches. We have designed and implemented BALL, the first object-oriented application framework for rapid prototyping in Molecular Modeling. By the use of the composite design pattern and polymorphism we were able to model the multitude of complex biochemical concepts in a well-structured and comprehensible class hierarchy, the BALL kernel classes. The isomorphism between the biochemical structures and the kernel classes leads to an intuitive interface. Since BALL was designed for rapid software prototyping, ease of use, extensibility, and robustness were our principal design goals. Besides the kernel classes, BALL provides fundamental components for import/export of data in various file formats, Molecular Mechanics simulations, three-dimensional visualization, and more complex ones like a numerical solver for the Poisson--Boltzmann equation.", acknowledgement = ack-nhfb, articleno = "16", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "libraries; molecular modeling; rapid software prototyping", } @Article{Brengel:2000:ESP, author = "Klaus Brengel and Andreas Crauser and Paolo Ferragina and Ulrich Meyer", title = "An experimental study of priority queues in external memory", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "5", pages = "17:1--17:??", month = "????", year = "2000", CODEN = "????", DOI = "http://doi.acm.org/10.1145/351827.384259", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:09 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper we compare the performance of eight different priority queue implementations: four of them are explicitly designed to work in an external-memory setting, the others are standard internal-memory queues available in the LEDA library [Mehlhorn and N{\"a}her 1999]. Two of the external-memory priority queues are obtained by engineering known internal-memory priority queues with the aim of achieving effective performance on external storage devices (i.e., Radix heaps [Ahuja et al. 1990] and array heaps [Thorup 1996]). Our experimental framework includes some simple tests, like random sequences of insert or delete-minimum operations, as well as more advanced tests consisting of intermixed sequences of update operations and 'application driven' update sequences originated by simulations of Dijkstra's algorithm on large graph instances. Our variegate spectrum of experimental results gives a good picture of the features of these priority queues, thus being helpful to anyone interested in the use of such data structures on very large data sets.", acknowledgement = ack-nhfb, articleno = "17", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Arge:2001:EAP, author = "Lars Arge and Laura Toma and Jeffrey Scott Vitter", title = "{I/O}-Efficient Algorithms for Problems on Grid-Based Terrains", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "1:1--1:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945395", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The potential and use of Geographic Information Systems is rapidly increasing due to the increasing availability of massive amounts of geospatial data from projects like NASA's Mission to Planet Earth. However, the use of these massive datasets also exposes scalability problems with existing GIS algorithms. These scalability problems are mainly due to the fact that most GIS algorithms have been designed to minimize internal computation time, while I/O communication often is the bottleneck when processing massive amounts of data. In this paper, we consider I/O-efficient algorithms for problems on grid-based terrains. Detailed grid-based terrain data is rapidly becoming available for much of the Earth's surface. We describe [EQUATION] I/O algorithms for several problems on [EQUATION] grids for which only $O(N)$ algorithms were previously known. Here $M$ denotes the size of the main memory and $B$ the size of a disk block. We demonstrate the practical merits of our work by comparing the empirical performance of our new algorithm for the {\em flow accumulation\/} problem with that of the previously best known algorithm. Flow accumulation, which models flow of water through a terrain, is one of the most basic hydrologic attributes of a terrain. We present the results of an extensive set of experiments on real-life terrain datasets of different sizes and characteristics. Our experiments show that while our new algorithm scales nicely with dataset size, the previously known algorithm 'breaks down' once the size of the dataset becomes bigger than the available main memory. For example, while our algorithm computes the flow accumulation for the Appalachian Mountains in about three hours, the previously known algorithm takes several weeks.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Demestrescu:2001:BCM, author = "Camil Demestrescu and Irene Finocchi", title = "Breaking cycles for minimizing crossings", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "2:1--2:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945396", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider the one-sided crossing minimization problem (CP): given a bipartite graph $G$ and a permutation $x_0$ of the vertices on a layer, find a permutation $x_1$ of the vertices on the other layer which minimizes the number of edge crossings in any straightline drawing of $G$ where vertices are placed on two parallel lines and sorted according to $x_0$ and $x_1$. Solving CP represents a fundamental step in the construction of aesthetically pleasing layouts of hierarchies and directed graphs, but unfortunately this problem has been proved to be NP-complete.\par In this paper we address the strong relation between CP and the problem of computing minimum feedback arc sets in directed graphs and we devise a new approximation algorithm for CP, called PM, that exploits this dependency. We experimentally and visually compare the performance of PM with the performance of well-known algorithms and of recent attractive strategies. Experiments are carried out on different families of randomly generated graphs, on pathological instances, and on real test sets. Performance indicators include both number of edge crossings and running time, as well as structural measures of the problem instances. We found CP to be a very interesting and rich problem from a combinatorial point of view. Our results clearly separate the behavior of the algorithms, proving the effectiveness of PM on most test sets and showing tradeoffs between quality of the solutions and running time. However, if the visual complexity of the drawings is considered, we found no clear winner. This confirms the importance of optimizing also other aesthetic criteria such as symmetry, edge length, and angular resolution.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "bipartite graphs; crossing minimization; experimental algorithms", } @Article{Gabow:2001:NFB, author = "Harold Gabow and Tadayoshi Kohno", title = "A Network-Flow-Based Scheduler: Design, Performance History, and Experimental Analysis", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "3:1--3:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945397", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We describe a program that schedules physician attending teams at Denver Health Medical Center. The program uses network flow techniques to prune an exponentially sized search space. We describe the program design, its performance history at the hospital, and experiments on a simplified version of the program.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "graphs; matroids; scheduling", } @Article{Iyer:2001:ESP, author = "Raj Iyer and David Karger and Hariharan Rahul and Mikkel Thorup", title = "An Experimental Study of Polylogarithmic, Fully Dynamic, Connectivity Algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "4:1--4:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945398", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present an experimental study of different variants of the amortized $O(\log^n)$-time fully-dynamic connectivity algorithm of Holm, de Lichtenberg, and Thorup (STOC'98). The experiments build upon experiments provided by Alberts, Cattaneo, and Italiano (SODA'96) on the randomized amortized $O(\log^3 n)$ fully-dynamic connectivity algorithm of Henzinger and King (STOC'95). Our experiments shed light upon similarities and differences between the two algorithms. We also present a slightly modified version of the Henzinger--King algorithm that runs in $O(\log^2 n)$ time, which resulted from our experiments.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Liberatore:2001:CSB, author = "Vincenzo Liberatore", title = "Caching and Scheduling for Broadcast Disk Systems", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "5:1--5:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945399", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Unicast connections lead to performance and scalability problems when a large client population attempts to access the same data. Broadcast push and broadcast disk technology address the problem by broadcasting data items from a server to a large number of clients. Broadcast disk performance depends mainly on caching strategies at the client site and on how the broadcast is scheduled at the server site. An on-line broadcast disk paging strategy makes caching decisions without knowing future page requests or access probabilities. This paper gives new implementations of existing on-line algorithms and reports on extensive empirical investigations. The gray algorithm [Khanna and Liberatore 2000] always outperformed other on-line strategies on both synthetic and Web traces. Moreover, caching limited the skewness of broadcast schedules, and led to favor efficient caching algorithms over refined scheduling strategies when the cache was large.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "broadcast disk; caching; scheduling", } @Article{Narasimhan:2001:GMS, author = "Giri Narasimhan and Martin Zachariasen", title = "Geometric Minimum Spanning Trees via Well-Separated Pair Decompositions", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "6:1--6:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945400", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Let $S$ be a set of $n$ points in $\Re^d$. We present an algorithm that uses the well-separated pair decomposition and computes the minimum spanning tree of $S$ under any $L_p$ or polyhedral metric. A theoretical analysis shows that it has an expected running time of $O(n \log n)$ for uniform point distributions; this is verified experimentally. Extensive experimental results show that this approach is practical. Under a variety of input distributions, the resulting implementation is robust and performs well for points in higher dimensional space.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Rahman:2001:ARS, author = "Naila Rahman and Rajeev Raman", title = "Adapting Radix Sort to the Memory Hierarchy", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "7:1--7:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945401", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We demonstrate the importance of reducing misses in the translation-lookaside buffer (TLB) for obtaining good performance on modern computer architectures. We focus on least-significant bit first (LSB) radix sort, standard implementations of which make many TLB misses. We give three techniques which simultaneously reduce cache and TLB misses for LSB radix sort: reducing working set size, explicit block transfer and pre-sorting. We note that: \item All the techniques above yield algorithms whose implementations outperform optimised cache-tuned implementations of LSB radix sort and comparison-based sorting algorithms. The fastest running times are obtained by the pre-sorting approach and these are over twice as fast as optimised cache-tuned implementations of LSB radix sort and quicksort. Even the simplest optimisation, using the TLB size to guide the choice of radix in standard implementations of LSB radix sort, gives good improvements over cache-tuned algorithms. \item One of the pre-sorting algorithms and explicit block transfer make few cache and TLB misses in the worst case. This is not true of standard implementations of LSB radix sort. We also apply these techniques to the problem of permuting an array of integers, and obtain gains of over 30\% relative to the naive algorithm by using explicit block transfer.", acknowledgement = ack-nhfb, articleno = "7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "cache; efficient sorting algorithms; external-memory algorithms; locality of reference; memory hierarchy; radix sort; translation-lookaside buffer (TLB)", } @Article{Stallmann:2001:HES, author = "Matthias Stallmann and Franc Brglez and Debabrata Ghosh", title = "Heuristics, Experimental Subjects, and Treatment Evaluation in Bigraph Crossing Minimization", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "8:1--8:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945402", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The bigraph crossing problem, embedding the two node sets of a bipartite graph along two parallel lines so that edge crossings are minimized, has applications to circuit layout and graph drawing. Experimental results for several previously known and two new heuristics suggest continued exploration of the problem, particularly sparse instances. We emphasize careful design of experimental subject classes and present novel views of the results. All source code, data, and scripts are available on-line", acknowledgement = ack-nhfb, articleno = "8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "crossing number; design of experiments; graph drawing; graph embedding; graph equivalence classes; layout", } @Article{Frigioni:2001:ESD, author = "Daniele Frigioni and Tobias Miller and Christos Zaroliagis", title = "An Experimental Study of Dynamic Algorithms for Transitive Closure", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "9:1--9:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945403", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We perform an extensive experimental study of several dynamic algorithms for transitive closure. In particular, we implemented algorithms given by Italiano, Yellin, Cicerone et al., and two recent randomized algorithms by Henzinger and King. We propose a fine-tuned version of Italiano's algorithms as well as a new variant of them, both of which were always faster than any of the other implementations of the dynamic algorithms. We also considered simple-minded algorithms that were easy to implement and likely to be fast in practice. Wetested and compared the above implementations on random inputs, on non-random inputs that are worst-case inputs for the dynamic algorithms, and on an input motivated by a real-world graph.", acknowledgement = ack-nhfb, articleno = "9", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dynamic algorithm; experimentation; transitive closure", } @Article{Matias:2001:EFP, author = "Yossi Matias and Nasir Rajpoot and Cenk Sahinalp", title = "The Effect of Flexible Parsing for Dynamic Dictionary-Based Data Compression", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "6", pages = "10:1--10:??", month = "????", year = "2001", CODEN = "????", DOI = "http://doi.acm.org/10.1145/945394.945404", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:03:55 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We report on the performance evaluation of greedy parsing with a single step lookahead (which we call flexible Parsing or {\em FP\/}) as an alternative to the commonly used greedy parsing (with no-lookaheads) scheme. Greedy parsing is the basis of most popular compression programs including UNIX {\tt compress} and {\tt gzip}, however it usually results in far from optimal parsing\slash compression with regard to the dictionary construction scheme in use. Flexible parsing, however, is optimal [MS99], i.e. partitions any given input to the smallest number of phrases possible, for dictionary construction schemes which satisfy the prefix property throughout their execution.\par We focus on the application of {\em FP\/} in the context of the LZW variant of the Lempel--Ziv'78 dictionary construction method [Wel84, ZL78], which is of considerable practical interest. We implement two compression algorithms which use (1) {\em FP\/} with LZW dictionary (LZW-{\em FP\/}), and (2) {\em FP\/} with an alternative flexible dictionary (FPA as introduced in [Hor95]). Our implementations are based on novel on-line data structures enabling us to use linear time and space. We test our implementations on a collection of input sequences which includes textual files, DNA sequences, medical images, and pseudorandom binary files, and compare our results with two of the most popular compression programs UNIX {\tt compress} and {\tt gzip}. Our results demonstrate that flexible parsing is especially useful for non-textual data, on which it improves over the compression rates of {\tt compress} and {\tt gzip} by up to 20\% and 35\%, respectively.", acknowledgement = ack-nhfb, articleno = "10", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Backes:2002:HLB, author = "Werner Backes and Susanne Wetzel", title = "Heuristics on lattice basis reduction in practice", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "1--1", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944619", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper we provide a survey on LLL lattice basis reduction in practice. We introduce several new heuristics as to speed up known lattice basis reduction methods and improve the quality of the computed reduced lattice basis in practice. We analyze substantial experimental data and to our knowledge, we are the first to present general heuristics for determining which variant of the reduction algorithm, for varied parameter choices, yields the most efficient reduction strategy for reducing a particular problem instance.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dynamic approximation; general reduction heuristics; lattice basis reduction; modular and iterative heuristics", } @Article{Iwama:2002:PLS, author = "Kazuo Iwama and Daisuke Kawai and Shuichi Miyazaki and Yasuo Okabe and Jun Umemoto", title = "Parallelizing local search for {CNF} satisfiability using vectorization and {PVM}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "2--2", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944620", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The purpose of this paper is to speed up the local search algorithm for the CNF Satisfiability problem. Our basic strategy is to run some 10$^5$ independent search paths simultaneously using PVM on a vector supercomputer VPP800, which consists of 40 vector processors. Using the above parallelization and vectorization together with some improvement of data structure, we obtained 600-times speedup in terms of the number of flips the local search can make per second, compared to the original GSAT by Selman and Kautz. We ran our parallel GSAT for benchmark instances and compared the running time with those of existing SAT programs. We could observe an apparent benefit of parallelization: Especially, we were able to solve two instances that have never been solved before this paper. We also tested parallel local search for the SAT encoding of the class scheduling problem. Again we were able to get almost the best answer in reasonable time.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; CNF Satisfiability; distributed computing; experimentation; local search algorithms; parallelization; PVM; vector supercomputer; vectorization", } @Article{Albers:2002:ESO, author = "Susanne Albers and Bianca Schr{\"o}der", title = "An experimental study of online scheduling algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "3--3", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944621", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present the first comprehensive experimental study of online algorithms for Graham's scheduling problem. Graham's scheduling problem is a fundamental problem in scheduling theory where a sequence of jobs has to be scheduled on $m$ identical parallel machines so as to minimize the makespan. Graham gave an elegant algorithm that is $(2 - 1 / m)$-competitive. Recently a number of new online algorithms were developed that achieve competitive ratios around 1.9. Since competitive analysis can only capture the worst case behavior of an algorithm a question often asked is: Are these new algorithms geared only towards a pathological case or do they perform better in practice, too?We address this question by analyzing the algorithms on various job sequences. In our actual tests, we analyzed the algorithms (1) on real world jobs and (2) on jobs generated by probability distributions. It turns out that the performance of the algorithms depends heavily on the characteristics of the respective work load. On job sequences that are generated by standard probability distributions, Graham's strategy is clearly the best. However, on the real world jobs the new algorithms often outperform Graham's strategy. Our experimental study confirms theoretical results in the sense that there are also job sequences in practice on which the new online algorithms perform better. Our study can help to inform practitioners about the new scheduling strategies as an alternative to Graham's algorithm.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; experimentation; online algorithms; performance; scheduling", } @Article{Mehlhorn:2002:IWM, author = "Kurt Mehlhorn and Guido Sch{\"a}fer", title = "Implementation of {$O(nm \log n)$} weighted matchings in general graphs: the power of data structures", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "4--4", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944622", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We describe the implementation of an algorithm which solves the weighted matching problem in general graphs with $n$ vertices and $m$ edges in time $O(nm \log n)$. Our algorithm is a variant of the algorithm of Galil, Micali and Gabow [Galil et al. 1986] and extensively uses sophisticated data structures, in particular {\em concatenable priority queues}, so as to reduce the time needed to perform dual adjustments and to find tight edges in Edmonds' blossom-shrinking algorithm. We compare our implementation to the experimentally fastest implementation, named {\em Blossom IV}, due to Cook and Rohe [Cook and Rohe 1997]. Blossom IV requires only very simple data structures and has an asymptotic running time of $O(n^2 m)$. Our experiments show that our new implementation is superior to Blossom IV. A closer inspection reveals that the running time of Edmonds' blossom-shrinking algorithm in practice heavily depends on the time spent to perform dual adjustments and to find tight edges. Therefore, optimizing these operations, as is done in our implementation, indeed speeds-up the practical performance of implementations of Edmonds' algorithm.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Edelkamp:2002:IHQ, author = "Stefan Edelkamp and Patrick Stiegeler", title = "Implementing {{\em HEAPSORT\/}} with $(n \log n - 0.9 n)$ and {{\em QUICKSORT}\/} with $(n \log n + 0.2 n)$ comparisons", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "5--5", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944623", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "With refinements to the {\em WEAK-HEAPSORT\/} algorithm we establish the general and practical relevant sequential sorting algorithm {\em INDEX-WEAK-HEAPSORT\/} with exactly $n \lceil \log n \rceil - 2^{\lceil \log n \rceil} + 1 \leq n \log n 0.9 n$ comparisons and at most $n \log n + 0.1 n$ transpositions on any given input. It comprises an integer array of size $n$ and is best used to generate an index for the data set. With {\em RELAXED-WEAK-HEAPSORT\/} and {\em GREEDY-WEAK-HEAPSORT\/} we discuss modifications for a smaller set of pending element transpositions. If extra space to create an index is not available, with {\em QUICK-WEAK-HEAPSORT\/} we propose an efficient {\em QUICKSORT\/} variant with $n \log n + 0.2 n + o(n)$ comparisons on the average. Furthermore, we present data showing that {\em WEAK-HEAPSORT, INDEX-WEAK-HEAPSORT\/} and {\em QUICK-WEAK-HEAPSORT\/} compete with other performant {\em QUICKSORT\/} and {\em HEAPSORT\/} variants.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Erlebach:2002:IAA, author = "Thomas Erlebach and Klaus Jansen", title = "Implementation of approximation algorithms for weighted and unweighted edge-disjoint paths in bidirected trees", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "6--6", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944624", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Given a set of weighted directed paths in a bidirected tree, the maximum weight edge-disjoint paths problem (MWEDP) is to select a subset of the given paths such that the selected paths are edge-disjoint and the total weight of the selected paths is maximized. MWEDP is {\em NP\/}-hard for bidirected trees of unbounded degree, even if all weights are the same (the unweighted case). Three different approximation algorithms are implemented: a known combinatorial $(5/3 + \epsilon)$-approximation algorithm $A_1$ for the unweighted case, a new combinatorial 2-approximation algorithm $A_2$ for the weighted case, and a known $(5 / 3 + \epsilon)$-approximation algorithm $A_3$ for the weighted case that is based on linear programming. For algorithm $A_1$, it is shown how efficient data structures can be used to obtain a worst-case running-time of $O(m + n + 4^{1/\epsilon} \sqrt n c m)$ for instances consisting of $m$ paths in a tree with $n$ nodes. Experimental results regarding the running-times and the quality of the solutions obtained by the three approximation algorithms are reported. Where possible, the approximate solutions are compared to the optimal solutions, which were computed by running CPLEX on an integer linear programming formulation of MWEDP.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; combinatorial optimization; experimentation; linear programming", } @Article{Lassous:2002:PLR, author = "Isabelle Gu{\'e}rin Lassous and Jens Gustedt", title = "Portable list ranking: an experimental study", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "7--7", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944625", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present and analyze two portable algorithms for the List Ranking Problem in the Coarse Grained Multicomputer model (CGM). We report on implementations of these algorithms and experiments that were done with these on a variety of parallel and distributed architectures, ranging from PC clusters to a mainframe parallel machine. With these experiments, we validate the chosen CGM model, and also show the possible gains and limits of such algorithms.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Vahrenhold:2002:PPL, author = "Jan Vahrenhold and Klaus H. Hinrichs", title = "Planar point location for large data sets: to seek or not to seek", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "8--8", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944626", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present an algorithm for external memory planar point location that is both effective and easy to implement. The base algorithm is an external memory variant of the bucket method by Edahiro, Kokubo and Asano that is combined with Lee and Yang's batched internal memory algorithm for planar point location. Although our algorithm is not optimal in terms of its worst-case behavior, we show its efficiency for both batched and single-shot queries by experiments with real-world data. The experiments show that the algorithm benefits from the mainly sequential disk access pattern and significantly outperforms the fastest algorithm for internal memory. Due to its simple concept, the algorithm can take advantage of multiple disks and processors in a rather straightforward yet efficient way.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Wickremesinghe:2002:ESU, author = "Rajiv Wickremesinghe and Lars Arge and Jeffrey S. Chase and Jeffrey Scott Vitter", title = "Efficient sorting using registers and caches", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "9--9", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944627", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Modern computer systems have increasingly complex memory systems. Common machine models for algorithm analysis do not reflect many of the features of these systems, e.g., large register sets, lockup-free caches, cache hierarchies, associativity, cache line fetching, and streaming behavior. Inadequate models lead to poor algorithmic choices and an incomplete understanding of algorithm behavior on real machines. A key step toward developing better models is to quantify the performance effects of features not reflected in the models. This paper explores the effect of memory system features on sorting performance. We introduce a new cache-conscious sorting algorithm, R-MERGE, which achieves better performance in practice over algorithms that are superior in the theoretical models. R-MERGE is designed to minimize memory stall cycles rather than cache misses by considering features common to many system designs.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Herrmann:2002:FCN, author = "Francine Herrmann and Alain Hertz", title = "Finding the chromatic number by means of critical graphs", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "10--10", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944628", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We propose a new exact algorithm for finding the chromatic number of a graph $G$. The algorithm attempts to determine the smallest possible induced subgraph $G'$ of $G$ which has the same chromatic number as $G$. Such a subgraph is said critical since all proper induced sub-graph of $G'$ have a chromatic number strictly smaller than $G'$. The proposed method is particularly helpful when a $k$-coloring of a non-critical graph is known, and it has to be proved that no $(k - 1)$-coloring of $G$ exists. Computational experiments on random graphs and on DIMACS benchmark problems demonstrate that the new proposed algorithm can solve larger problem than previous known exact methods.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; experimentation; performance", } @Article{Fekete:2002:SHP, author = "S{\'a}ndor P. Fekete and Henk Meijer and Andr{\'e} Rohe and Walter Tietze", title = "Solving a 'Hard' problem to approximate an 'Easy' one: heuristics for maximum matchings and maximum traveling salesman problems", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "11--11", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944629", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider geometric instances of the Maximum Weighted Matching Problem (MWMP) and the Maximum Traveling Salesman Problem (MTSP) with up to 3,000,000 vertices. Making use of a geometric duality relationship between MWMP, MTSP, and the Fermat--Weber-Problem (FWP), we develop a heuristic approach that yields in near-linear time solutions as well as upper bounds. Using various computational tools, we get solutions within considerably less than 1\% of the optimum. An interesting feature of our approach is that, even though an FWP is hard to compute in theory and Edmonds' algorithm for maximum weighted matching yields a polynomial solution for the MWMP, the practical behavior is just the opposite, and we can solve the FWP with high accuracy in order to find a good heuristic solution for the MWMP.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "approximation; Fermat--Weber problem; geometric optimization; geometric problems; heuristics; maximum traveling salesman problem (MTSP); maximum weighted matching; near-linear algorithms", } @Article{Neri:2002:RCL, author = "Filippo Neri", title = "Relational concept learning by cooperative evolution", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "7", pages = "12--12", month = "????", year = "2002", CODEN = "????", DOI = "http://doi.acm.org/10.1145/944618.944630", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Concept learning is a computationally demanding task that involves searching large hypothesis spaces containing candidate descriptions. Stochastic search combined with parallel processing provide a promising approach to successfully deal with such computationally intensive tasks. Learning systems based on distributed genetic algorithms (GA) were able to find concept descriptions as accurate as the ones found by state-of-the-art learning systems based on alternative approaches. However, genetic algorithms' exploitation has the drawback of being computationally demanding. We show how a suitable architectural choice, named cooperative evolution, allows to solve complex applications in an acceptable user waiting time and with a reasonable computational cost by using GA-based learning systems because of the effective exploitation of distributed computation. A variety of experimental settings is analyzed and an explanation for the empirical observations is proposed.", acknowledgement = ack-nhfb, fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "distributed genetic algorithm; first order logic concept learning; relational concept learning", } @Article{Kumar:2003:AME, author = "Piyush Kumar and Joseph S. B. Mitchell and E. Alper Yildirim", title = "Approximate minimum enclosing balls in high dimensions using core-sets", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "8", pages = "1.1:1--1.1:??", month = "????", year = "2003", CODEN = "????", DOI = "http://doi.acm.org/10.1145/996546.996548", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:56 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study the minimum enclosing ball (MEB) problem for sets of points or balls in high dimensions. Using techniques of second-order cone programming and 'core-sets', we have developed $(1 + \epsilon)$-approximation algorithms that perform well in practice, especially for very high dimensions, in addition to having provable guarantees. We prove the existence of core-sets of size $O(1/\epsilon)$, improving the previous bound of $O(1/\epsilon^2)$, and we study empirically how the core-set size grows with dimension. We show that our algorithm, which is simple to implement, results in fast computation of nearly optimal solutions for point sets in much higher dimension than previously computable using exact techniques.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "approximation algorithms; minimum enclosing ball; second-order cone programming", } @Article{Arge:2003:EPL, author = "Lars Arge and Andrew Danner and Sha-Mayn Teh", title = "{I/O}-efficient point location using persistent {B}-trees", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "8", pages = "1.2:1--1.2:??", month = "????", year = "2003", CODEN = "????", DOI = "http://doi.acm.org/10.1145/996546.996549", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:56 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present an external planar point location data structure that is I/O-efficient both in theory and practice. The developed structure uses linear space and answers a query in optimal $O(\log B N)$ I/Os, where $B$ is the disk block size. It is based on a persistent B-tree, and all previously developed such structures assume a total order on the elements in the structure. As a theoretical result of independent interest, we show how to remove this assumption. Most previous theoretical I/O-efficient planar point location structures are relatively complicated and have not been implemented. Based on a bucket approach, Vahrenhold and Hinrichs therefore developed a simple and practical, but theoretically non-optimal, heuristic structure. We present an extensive experimental evaluation that shows that, on a range of real-world Geographic Information Systems (GIS) data, our structure uses a similar number of I/Os as the structure of Vahrenhold and Hinrichs to answer a query. On a synthetically generated worst-case dataset our structure uses significantly fewer I/Os.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Buchsbaum:2003:FPM, author = "Adam L. Buchsbaum and Glenn S. Fowler and Balachannder Kirishnamurthy and Kiem-Phong Vo and Jia Wang", title = "Fast prefix matching of bounded strings", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "8", pages = "1.3:1--1.3:??", month = "????", year = "2003", CODEN = "????", DOI = "http://doi.acm.org/10.1145/996546.996550", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:56 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Longest Prefix Matching (LPM) is the problem of finding which string from a given set is the longest prefix of another, given string. LPM is a core problem in many applications, including IP routing, network data clustering, and telephone network management. These applications typically require very fast matching of bounded strings, i.e., strings that are short and based on small alphabets. We note a simple correspondence between bounded strings and natural numbers that maps prefixes to nested intervals so that computing the longest prefix matching a string is equivalent to finding the shortest interval containing its corresponding integer value. We then present {\em retries}, a fast and compact data structure for LPM on general alphabets. Performance results show that retries often outperform previously published data structures for IP look-up. By extending LPM to general alphabets, retries admit new applications that could not exploit prior LPM solutions designed for IP look-ups.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "IP routing; prefix matching; table look-up; tries", } @Article{Breimer:2003:LAL, author = "Eric A. Breimer and Mark K. Goldberg and Darren T. Lim", title = "A learning algorithm for the longest common subsequence problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "8", pages = "2.1:1--2.1:??", month = "????", year = "2003", CODEN = "????", DOI = "http://doi.acm.org/10.1145/996546.996552", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:56 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present an experimental study of a learning algorithm for the longest common subsequence problem, {\em LCS}. Given an arbitrary input domain, the algorithm learns an {\em LCS\/}-procedure tailored to that domain. The learning is done with the help of an oracle, which can be any {\em LCS\/}-algorithm. After solving a limited number of training inputs using an oracle, the learning algorithm outputs a new {\em LCS\/}-procedure. Our experiments demonstrate that, by allowing a slight loss of optimality, learning yields a procedure which is significantly faster than the oracle. The oracle used for the experiments is the {\em np\/}-procedure by Wu {\em et al.}, a modification of Myers' classical {\em LCS\/}-algorithm. We show how to scale up the results of learning on small inputs to inputs of arbitrary lengths. For the domain of two random 2-symbol inputs of length $n$, learning yields a program with 0.999 expected accuracy, which runs in $O(n^{1.41})$-time, in contrast with $O(n^2 \log n)$ running time of the fastest theoretical algorithm that produces optimal solutions. For the domain of random 2-symbol inputs of length 100,000, the program runs 10.5 times faster than the {\em np\/}-procedure, producing 0.999- accurate outputs. The scaled version of the evolved algorithm applied to random inputs of length 1 million runs approximately 30 times faster than the {\em np\/}-procedure while constructing 0.999- accurate solutions. We apply the evolved algorithm to DNA sequences of various lengths by training on random 4-symbol sequences of up to length 10,000. The evolved algorithm, scaled up to the lengths of up to 1.8 million, produces solutions with the 0.998-accuracy in a fraction of the time used by the {\em np}.", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Venkataraman:2003:BAP, author = "Gayathri Venkataraman and Sartaj Sahni and Srabani Mukhopadhyaya", title = "A blocked all-pairs shortest-paths algorithm", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "8", pages = "2.2:1--2.2:??", month = "????", year = "2003", CODEN = "????", DOI = "http://doi.acm.org/10.1145/996546.996553", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:56 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We propose a blocked version of Floyd's all-pairs shortest-paths algorithm. The blocked algorithm makes better utilization of cache than does Floyd's original algorithm. Experiments indicate that the blocked algorithm delivers a speedup (relative to the unblocked Floyd's algorithm) between 1.6 and 1.9 on a Sun Ultra Enterprise 4000/5000 for graphs that have between 480 and 3200 vertices. The measured speedup on an SGI O2 for graphs with between 240 and 1200 vertices is between 1.6 and 2.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "all pairs shortest paths; blocking; cache; speedup", } @Article{Petit:2003:EML, author = "Jordi Petit", title = "Experiments on the minimum linear arrangement problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "8", pages = "2.3:1--2.3:??", month = "????", year = "2003", CODEN = "????", DOI = "http://doi.acm.org/10.1145/996546.996554", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:04:56 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "This paper deals with the Minimum Linear Arrangement problem from an experimental point of view. Using a testsuite of sparse graphs, we experimentally compare several algorithms to obtain upper and lower bounds for this problem. The algorithms considered include Successive Augmentation heuristics, Local Search heuristics and Spectral Sequencing. The testsuite is based on two random models and 'real life' graphs. As a consequence of this study, two main conclusions can be drawn: On one hand, the best approximations are usually obtained using Simulated Annealing, which involves a large amount of computation time. Solutions found with Spectral Sequencing are close to the ones found with Simulated Annealing and can be obtained in significantly less time. On the other hand, we notice that there exists a big gap between the best obtained upper bounds and the best obtained lower bounds. These two facts together show that, in practice, finding lower and upper bounds for the Minimum Linear Arrangement problem is hard.", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Brandes:2004:GNC, author = "Ulrik Brandes and Frank Schulz and Dorothea Wagner and Thomas Willhalm", title = "Generating node coordinates for shortest-path computations in transportation networks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "9", pages = "1.1:1--1.1:??", month = "????", year = "2004", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1005813.1005815", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:22 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Speed-up techniques that exploit given node coordinates have proven useful for shortest-path computations in transportation networks and geographic information systems. To facilitate the use of such techniques when coordinates are missing from some, or even all, of the nodes in a network we generate artificial coordinates using methods from graph drawing. Experiments on a large set of German train timetables indicate that the speed-up achieved with coordinates from our drawings is close to that achieved with the true coordinates---and in some special cases even better.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "graph drawing; shortest paths; transportation networks; travel planning", } @Article{Niewiadomski:2004:PSD, author = "Robert Niewiadomski and Jos{\'e} Nelson Amaral and Robert C. Holte", title = "A performance study of data layout techniques for improving data locality in refinement-based pathfinding", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "9", pages = "1.2:1--1.2:??", month = "????", year = "2004", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1005813.1041511", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:22 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The widening gap between processor speed and memory latency increases the importance of crafting data structures and algorithms to exploit temporal and spatial locality. Refinement-based pathfinding algorithms, such as Classic Refinement (CR), find quality paths in very large sparse graphs where traditional search techniques fail to generate paths in acceptable time. In this paper, we present a performance evaluation study of three simple data structure transformations aimed at improving the data reference locality of CR. These transformations are robust to changes in computer architecture and the degree of compiler optimization. We test our alternative designs on four contemporary architectures, using two compilers for each machine. In our experiments, the application of these techniques results in performance improvements of up to 67\% with consistent improvements above 15\%. Analysis reveals that these improvements stem from improved data reference locality at the page level and to a lesser extent at the cache line level.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "cache-conscious algorithms; classical refinement; pathfinding", } @Article{Marathe:2004:ESS, author = "Madhav V. Marathe and Alessandro Panconesi and Larry D. {Risinger, Jr.}", title = "An experimental study of a simple, distributed edge-coloring algorithm", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "9", pages = "1.3:1--1.3:??", month = "????", year = "2004", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1005813.1041515", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:22 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We conduct an experimental analysis of a distributed randomized algorithm for edge coloring simple undirected graphs. The algorithm is extremely simple yet, according to the probabilistic analysis, it computes nearly optimal colorings very quickly [Grable and Panconesi 1997]. We test the algorithm on a number of random as well as nonrandom graph families. The test cases were chosen based on two objectives: (i) to provide insights into the worst-case behavior (in terms of time and quality) of the algorithm and (ii) to test the performance of the algorithm with instances that are likely to arise in practice. Our main results include the following:(1) The empirical results obtained compare very well with the recent empirical results reported by other researchers [Durand et al. 1994, 1998; Jain and Werth 1995].(2) The empirical results confirm the bounds on the running time and the solution quality as claimed in the theoretical paper. Our results show that for certain classes of graphs the algorithm is likely to perform much better than the analysis suggests.(3) The results demonstrate that the algorithm might be well suited (from a theoretical as well as practical standpoint) for edge coloring graphs quickly and efficiently in a distributed setting. Based on our empirical study, we propose a simple modification of the original algorithm with substantially improved performance in practice.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "distributed algorithms; edge coloring; experimental analysis of algorithms; high performance computing; randomized algorithms; scheduling", } @Article{Fredriksson:2004:AOS, author = "Kimmo Fredriksson and Gonzalo Navarro", title = "Average-optimal single and multiple approximate string matching", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "9", pages = "1.4:1--1.4:??", month = "????", year = "2004", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1005813.1041513", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:22 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present a new algorithm for multiple approximate string matching. It is based on reading backwards enough l-grams from text windows so as to prove that no occurrence can contain the part of the window read, and then shifting the window. We show analytically that our algorithm is optimal on average. Hence our first contribution is to fill an important gap in the area, since no average-optimal algorithm existed for multiple approximate string matching. We consider several variants and practical improvements to our algorithm, and show experimentally that they are resistant to the number of patterns and the fastest for low difference ratios, displacing the long-standing best algorithms. Hence our second contribution is to give a practical algorithm for this problem, by far better than any existing alternative in many cases of interest. On real-life texts, our algorithm is especially interesting for computational biology applications. In particular, we show that our algorithm can be successfully used to search for one pattern, where many more competing algorithms exist. Our algorithm is also average-optimal in this case, being the second after that of Chang and Marr. However, our algorithm permits higher difference ratios than Chang and Marr, and this is our third contribution. In practice, our algorithm is competitive in this scenario too, being the fastest for low difference ratios and moderate alphabet sizes. This is our fourth contribution, which also answers affirmatively the question of whether a practical average-optimal approximate string-matching algorithm existed.", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; approximate string matching; biological sequences; multiple string matching; optimality", } @Article{Sinha:2004:CCS, author = "Ranjan Sinha and Justin Zobel", title = "Cache-conscious sorting of large sets of strings with dynamic tries", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "9", pages = "1.5:1--1.5:??", month = "????", year = "2004", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1005813.1041517", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:22 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Ongoing changes in computer architecture are affecting the efficiency of string-sorting algorithms. The size of main memory in typical computers continues to grow but memory accesses require increasing numbers of instruction cycles, which is a problem for the most efficient of the existing string-sorting algorithms as they do not utilize cache well for large data sets. We propose a new sorting algorithm for strings, burstsort, based on dynamic construction of a compact trie in which strings are kept in buckets. It is simple, fast, and efficient. We experimentally explore key implementation options and compare burstsort to existing string-sorting algorithms on large and small sets of strings with a range of characteristics. These experiments show that, for large sets of strings, burstsort is almost twice as fast as any previous algorithm, primarily due to a lower rate of cache miss.", acknowledgement = ack-nhfb, articleno = "1.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Goh:2004:TAP, author = "Rick Siow Mong Goh and Ian Li-Jin Thng", title = "Twol-amalgamated priority queues", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "9", pages = "1.6:1--1.6:??", month = "????", year = "2004", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1005813.1057625", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:22 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Priority queues are essential function blocks in numerous applications such as discrete event simulations. This paper describes and exemplifies the ease of obtaining high performance priority queues using a two-tier list-based structure. This new implementation, called the {\em Twol\/} structure, is amalgamated with three priority queues, namely, the Henriksen's queue, splay tree and skew heap, to enhance the efficiency of these {\em basal\/} priority queue structures. Using a model that combines traditional average case and amortized complexity analysis, Twol-amalgamated priority queues that maintain $N$ active events are theoretically proven to offer $O(1)$ {\em expected amortized complexity\/} under reasonable assumptions. They are also demonstrated empirically to offer stable near $O(1)$ performance for widely varying priority increment distributions and for queue sizes ranging from 10 to 10 million. Extensive empirical results show that the Twol-amalgamated priority queues consistently outperform those basal structures (i.e., without the Twol structure) with an average speedup of about three to five times on widely different hardware architectures. These results provide testimony that the Twol-amalgamated priority queues are suitable for implementation in sizable application scenarios such as, but not limited to, large-scale discrete event simulation.", acknowledgement = ack-nhfb, articleno = "1.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithm analysis; calendar queue; discrete event simulation; future event list; Henriksen's; pending event set; priority queue; simulator; skew heap; splay tree; tree", } @Article{Ioannidis:2005:ADS, author = "Ioannis Ioannidis and Ananth Grama and Mikhail Atallah", title = "Adaptive data structures for {IP} lookups", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "1.1:1--1.1:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1064548", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The problem of efficient data structures for IP lookups has been well studied in the literature. Techniques such as LC tries and extensible hashing are commonly used. In this paper, we address the problem of generalizing LC tries, based on traces of past lookups, to provide performance guarantees for memory suboptimal structures. As a specific example, if a memory-optimal (LC) trie takes 6 MB and the total memory at the router is 8 MB, how should the trie be modified to make best use of the 2 MB of excess memory? We present a greedy algorithm for this problem and prove that, if for the optimal data structure there are $b$ fewer memory accesses on average for each lookup compared with the original trie, the solution produced by the greedy algorithm will have at least $9 \times b /11$ fewer memory accesses on average (compared to the original trie). An efficient implementation of this algorithm presents significant additional challenges. We describe an implementation with a time complexity of $O(\xi(d) n \log n)$ and a space complexity of $O(n)$, where $n$ is the number of nodes of the trie and $d$ its depth. The depth of a trie is fixed for a given version of the Internet protocol and is typically $O(\log n)$. In this case, $\xi(d) = O(\log^2 n)$. We also demonstrate experimentally the performance and scalability of the algorithm on actual routing data.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "IP lookups; level compression", } @Article{Lesh:2005:NHI, author = "N. Lesh and J. Marks and A. McMahon and M. Mitzenmacher", title = "New heuristic and interactive approaches to {$2$D} rectangular strip packing", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "1.2:1--1.2:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1083322", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper, we consider the two-dimensional rectangular strip packing problem. A standard simple heuristic, Bottom-Left-Decreasing (BLD), has been shown to perform quite well in practice. We introduce and demonstrate the effectiveness of BLD*, a stochastic search variation of BLD. While BLD places the rectangles in decreasing order of height, width, area, and perimeter, BLD* successively tries random orderings, chosen from a distribution determined by their Kendall-tau distance from one of these fixed orderings. Our experiments on benchmark problems show that BLD* produces significantly better packings than BLD after only 1 min of computation. Furthermore, we also show that BLD* outperforms recently reported metaheuristics. Furthermore, we observe that people seem able to reason about packing problems extremely well. We incorporate our new algorithms in an interactive system that combines the advantages of computer speed and human reasoning. Using the interactive system, we are able to quickly produce significantly better solutions than BLD* by itself.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "2D rectangular strip packing; cutting stock/trim; interactive methods", } @Article{Wagner:2005:GCE, author = "Dorothea Wagner and Thomas Willhalm and Christos Zaroliagis", title = "Geometric containers for efficient shortest-path computation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "1.3:1--1.3:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1103378", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A fundamental approach in finding efficiently best routes or optimal itineraries in traffic information systems is to reduce the search space (part of graph visited) of the most commonly used shortest path routine (Dijkstra's algorithm) on a suitably defined graph. We investigate reduction of the search space while simultaneously retaining data structures, created during a preprocessing phase, of size linear (i.e., optimal) to the size of the graph. We show that the search space of Dijkstra's algorithm can be significantly reduced by extracting geometric information from a given layout of the graph and by encapsulating precomputed shortest-path information in resulted geometric objects (containers). We present an extensive experimental study comparing the impact of different types of geometric containers using test data from real-world traffic networks. We also present new algorithms as well as an empirical study for the dynamic case of this problem, where edge weights are subject to change and the geometric containers have to be updated and show that our new methods are two to three times faster than recomputing everything from scratch. Finally, in an appendix, we discuss the software framework that we developed to realize the implementations of all of our variants of Dijkstra's algorithm. Such a framework is not trivial to achieve as our goal was to maintain a common code base that is, at the same time, small, efficient, and flexible, as we wanted to enhance and combine several variants in any possible way.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "data structures and algorithms; Dijkstra's algorithm; geometric container; graph algorithms; shortest path; traffic network", } @Article{Lopez-Ortiz:2005:FSS, author = "Alejandro L{\'o}pez-Ortiz and Mehdi Mirzazadeh and Mohammad Ali Safari and Hossein Sheikhattar", title = "Fast string sorting using order-preserving compression", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "1.4:1--1.4:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180611", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We give experimental evidence for the benefits of order-preserving compression in sorting algorithms. While, in general, any algorithm might benefit from compressed data because of reduced paging requirements, we identified two natural candidates that would further benefit from order-preserving compression, namely string-oriented sorting algorithms and word-RAM algorithms for keys of bounded length. The word-RAM model has some of the fastest known sorting algorithms in practice. These algorithms are designed for keys of bounded length, usually 32 or 64 bits, which limits their direct applicability for strings. One possibility is to use an order-preserving compression scheme, so that a bounded-key-length algorithm can be applied. For the case of standard algorithms, we took what is considered to be the among the fastest nonword RAM string sorting algorithms, Fast MKQSort, and measured its performance on compressed data. The Fast MKQSort algorithm of Bentley and Sedgewick is optimized to handle text strings. Our experiments show that order-compression techniques results in savings of approximately 15\% over the same algorithm on noncompressed data. For the word-RAM, we modified Andersson's sorting algorithm to handle variable-length keys. The resulting algorithm is faster than the standard Unix sort by a factor of 1.5 $X$. Last, we used an order-preserving scheme that is within a constant additive term of the optimal Hu--Tucker, but requires linear time rather than $O(m \log m)$, where $m = |\Sigma|$ is the size of the alphabet.", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "order-preserving compression; sorting; unit-cost RAM; word-RAM", } @Article{Ribeiro:2005:P, author = "Celso C. Ribeiro and Simone L. Martins", title = "Preface", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.1:1--2.1:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180620", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Sinha:2005:URS, author = "Ranjan Sinha and Justin Zobel", title = "Using random sampling to build approximate tries for efficient string sorting", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.10:1--2.10:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180622", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Algorithms for sorting large datasets can be made more efficient with careful use of memory hierarchies and reduction in the number of costly memory accesses. In earlier work, we introduced burstsort, a new string-sorting algorithm that on large sets of strings is almost twice as fast as previous algorithms, primarily because it is more cache efficient. Burstsort dynamically builds a small trie that is used to rapidly allocate each string to a bucket. In this paper, we introduce new variants of our algorithm: SR-burstsort, DR-burstsort, and DRL-burstsort. These algorithms use a random sample of the strings to construct an approximation to the trie prior to sorting. Our experimental results with sets of over 30 million strings show that the new variants reduce, by up to 37\%, cache misses further than did the original burstsort, while simultaneously reducing instruction counts by up to 24\%. In pathological cases, even further savings can be obtained.", acknowledgement = ack-nhfb, articleno = "2.10", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "cache-aware; cache-conscious; data structure; in-memory; sorting; string", } @Article{Bracht:2005:GAA, author = "Evandro C. Bracht and Luis and A. A. Meira and F. K. Miyazawa", title = "A greedy approximation algorithm for the uniform metric labeling problem analyzed by a primal-dual technique", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.11:1--2.11:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180623", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider the uniform metric labeling problem. This NP-hard problem considers how to assign objects to labels respecting assignment and separation costs. The known approximation algorithms are based on solutions of large linear programs and are impractical for moderate- and large-size instances. We present an 8log $n$-approximation algorithm that can be applied to large-size instances. The algorithm is greedy and is analyzed by a primal-dual technique. We implemented the presented algorithm and two known approximation algorithms and compared them at randomized instances. The gain of time was considerable with small error ratios. We also show that the analysis is tight, up to a constant factor.", acknowledgement = ack-nhfb, articleno = "2.11", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "approximation algorithms; graph labeling", } @Article{deSouza:2005:DMP, author = "Cid C. de Souza and Andre M. Lima and Guido Araujo and Nahri B. Moreano", title = "The datapath merging problem in reconfigurable systems: {Complexity}, dual bounds and heuristic evaluation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.2:1--2.2:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180613", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper, we investigate the data path merging problem (DPM) in reconfigurable systems. DPM is modeled as a graph optimization problem and is shown to be {\em NP\/}-hard. An Integer Programming (IP) formulation of the problem is presented and some valid inequalities for the convex hull of integer solutions are introduced. These inequalities form the basis of a branch-and-cut algorithm that we implemented. This algorithm was used to compute lower bounds for a set of DPM instances, allowing us to assess the performance of two heuristics proposed earlier in the literature for the problem. Moreover, the branch-and-cut algorithm also was proved to be a valuable tool to solve small-sized DPM instances to optimality.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "data path merging; heuristics; lower bounds; reconfigurable systems", } @Article{Du:2005:IAA, author = "Jingde Du and Stavros G. Kolliopoulos", title = "Implementing approximation algorithms for the single-source unsplittable flow problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.3:1--2.3:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180614", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In the {\em single-source unsplittable flow\/} problem, commodities must be routed simultaneously from a common source vertex to certain sinks in a given graph with edge capacities. The demand of each commodity must be routed along a single path so that the total flow through any edge is at most, its capacity. This problem was introduced by Kleinberg [1996a] and generalizes several NP-complete problems. A cost value per unit of flow may also be defined for every edge. In this paper, we implement the 2-approximation algorithm of Dinitz et al. [1999] for congestion, which is the best known, and the (3, 1)-approximation algorithm of Skutella [2002] for congestion and cost, which is the best known bicriteria approximation. We experimentally study the quality of approximation achieved by the algorithms and the effect of heuristics on their performance. We also compare these algorithms against the previous best ones by Kolliopoulos and Stein [1999].", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "approximation algorithms; network flow; unsplittable flow", } @Article{Duch:2005:IPM, author = "Amalia Duch and Conrado Mart{\'\i}nez", title = "Improving the performance of multidimensional search using fingers", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.4:1--2.4:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180615", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We propose two variants of $K$-d trees where {\em fingers\/} are used to improve the performance of orthogonal range search and nearest neighbor queries when they exhibit locality of reference. The experiments show that the second alternative yields significant savings. Although it yields more modest improvements, the first variant does it with much less memory requirements and great simplicity, which makes it more attractive on practical grounds.", acknowledgement = ack-nhfb, articleno = "2.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "experimental algorithmics; Finger search; K-d trees; locality; multidimensional data structures; nearest-neighbors searching; orthogonal range searching", } @Article{Holzer:2005:CST, author = "Martin Holzer and Frank Schulz and Dorothea Wagner and Thomas Willhalm", title = "Combining speed-up techniques for shortest-path computations", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.5:1--2.5:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180616", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In practice, computing a shortest path from one node to another in a directed graph is a very common task. This problem is classically solved by Dijkstra's algorithm. Many techniques are known to speed up this algorithm heuristically, while optimality of the solution can still be guaranteed. In most studies, such techniques are considered individually. The focus of our work is {\em combination\/} of speed-up techniques for Dijkstra's algorithm. We consider all possible combinations of four known techniques, namely, {\em goal-directed search}, {\em bidirectional search}, {\em multilevel approach}, and {\em shortest-path containers}, and show how these can be implemented. In an extensive experimental study, we compare the performance of the various combinations and analyze how the techniques harmonize when jointly applied. Several real-world graphs from road maps and public transport and three types of generated random graphs are taken into account.", acknowledgement = ack-nhfb, articleno = "2.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "combination; Dijkstra's algorithm; shortest path; speed-up", } @Article{Hyyro:2005:IBP, author = "Heikki Hyyr{\"o} and Kimmo Fredriksson and Gonzalo Navarro", title = "Increased bit-parallelism for approximate and multiple string matching", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.6:1--2.6:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180617", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Bit-parallelism permits executing several operations simultaneously over a set of bits or numbers stored in a single computer word. This technique permits searching for the approximate occurrences of a pattern of length $m$ in a text of length $n$ in time $O(\lceil m / w \rceil n)$, where $w$ is the number of bits in the computer word. Although this is asymptotically the optimal bit-parallel speedup over the basic $O(mn)$ time algorithm, it wastes bit-parallelism's power in the common case where $m$ is much smaller than $w$, since $w - m$ bits in the computer words are unused. In this paper, we explore different ways to increase the bit-parallelism when the search pattern is short. First, we show how multiple patterns can be packed into a single computer word so as to search for all them simultaneously. Instead of spending $O(rn)$ time to search for $r$ patterns of length $m \leq w / 2$, we need $O(\lceil rm / w \rceil n)$ time. Second, we show how the mechanism permits boosting the search for a single pattern of length $m \leq w / 2$, which can be searched for in $O(\lceil n / \lfloor w / m \rfloor \rceil)$ bit-parallel steps instead of $O(n)$. Third, we show how to extend these algorithms so that the time bounds essentially depend on $k$ instead of $m$, where $k$ is the maximum number of differences permitted. Finally, we show how the ideas can be applied to other problems such as multiple exact string matching and one-against-all computation of edit distance and longest common subsequences. Our experimental results show that the new algorithms work well in practice, obtaining significant speedups over the best existing alternatives, especially on short patterns and moderate number of differences allowed. This work fills an important gap in the field, where little work has focused on very short patterns.", acknowledgement = ack-nhfb, articleno = "2.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "approximate string matching; bit-parallelism; multiple string matching", } @Article{Nikolov:2005:SEH, author = "Nikola S. Nikolov and Alexandre Tarassov and J{\"u}rgen Branke", title = "In search for efficient heuristics for minimum-width graph layering with consideration of dummy nodes", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.7:1--2.7:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180618", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We propose two fast heuristics for solving the NP-hard problem of graph layering with the minimum width and consideration of dummy nodes. Our heuristics can be used at the layer-assignment phase of the Sugiyama method for drawing of directed graphs. We evaluate our heuristics by comparing them to the widely used fast-layering algorithms in an extensive computational study with nearly 6000 input graphs. We also demonstrate how the well-known longest-path and Coffman--Graham algorithms can be used for finding narrow layerings with acceptable aesthetic properties.", acknowledgement = ack-nhfb, articleno = "2.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dummy vertices; hierarchical graph drawing; layer assignment; layered graphs; layering", } @Article{Pemmaraju:2005:AIC, author = "Sriram V. Pemmaraju and Sriram Penumatcha and Rajiv Raman", title = "Approximating interval coloring and max-coloring in chordal graphs", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.8:1--2.8:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180619", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider two coloring problems: interval coloring and max-coloring for chordal graphs. Given a graph $G = (V, E)$ and positive-integral vertex weights $w: V \rightarrow N$, the {\em interval-coloring\/} problem seeks to find an assignment of a real interval $I(u)$ to each vertex $u \in V$, such that two constraints are satisfied: (i) for every vertex $u \in V$, $|I(u)| = w(u)$ and (ii) for every pair of adjacent vertices $u$ and $v$, $I(u) \cap I(v) = \emptyset$. The goal is to minimize the {\em span\/} $|\cup_{v \in V} I(v)|$. The {\em max-coloring problem\/} seeks to find a proper vertex coloring of $G$ whose color classes $C_1$, $C_2$, \ldots{}, $C_k$, minimize the sum of the weights of the heaviest vertices in the color classes, that is, $\sum^k_i = 1 \hbox{max}_{v \epsilon C i w (v)}$. Both problems arise in efficient memory allocation for programs. The interval-coloring problem models the compile-time memory allocation problem and has a rich history dating back at least to the 1970s. The max-coloring problem arises in minimizing the total buffer size needed by a dedicated memory manager for programs. In another application, this problem models scheduling of conflicting jobs in batches to minimize the {\em makespan}. Both problems are NP-complete even for interval graphs, although there are constant-factor approximation algorithms for both problems on interval graphs. In this paper, we consider these problems for {\em chordal graphs}, a subclass of perfect graphs. These graphs naturally generalize interval graphs and can be defined as the class of graphs that have no induced cycle of length $> 3$. Recently, a 4-approximation algorithm (which we call GeomFit) has been presented for the max-coloring problem on perfect graphs (Pemmaraju and Raman 2005). This algorithm can be used to obtain an interval coloring as well, but without the constant-factor approximation guarantee. In fact, there is no known constant-factor approximation algorithm for the interval-coloring problem on perfect graphs. We study the performance of GeomFit and several simple $O(\log(n))$-factor approximation algorithms for both problems. We experimentally evaluate and compare four simple heuristics: first-fit, best-fit, GeomFit, and a heuristic based on partitioning the graph into vertex sets of similar weight. Both for max-coloring and for interval coloring, GeomFit deviates from OPT by about 1.5\%, on average. The performance of first-fit comes close second, deviating from OPT by less than 6\%, on average, for both problems. Best-fit comes third and graph-partitioning heuristic comes a distant last. Our basic data comes from about 10,000 runs of each of the heuristics for each of the two problems on randomly generated chordal graphs of various sizes, sparsity, and structure.", acknowledgement = ack-nhfb, articleno = "2.8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "chordal graphs; dynamic storage allocation; graph coloring; perfect graphs", } @Article{Santos:2005:TSH, author = "Haroldo G. Santos and Luiz S. Ochi and Marcone J. F. Souza", title = "A {Tabu} search heuristic with efficient diversification strategies for the class\slash teacher timetabling problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "10", pages = "2.9:1--2.9:??", month = "????", year = "2005", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1064546.1180621", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:05:40 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The Class/Teacher Timetabling Problem (CTTP) deals with the weekly scheduling of encounters between teachers and classes of an educational institution. Since CTTP is a NP-hard problem for nearly all of its variants, the use of heuristic methods for its resolution is justified. This paper presents an efficient Tabu Search (TS) heuristic with two different memory based diversification strategies for CTTP. Results obtained through an application of the method to a set of real world problems show that it produces better solutions than a previously proposed TS found in the literature and faster times are observed in the production of good quality solutions.", acknowledgement = ack-nhfb, articleno = "2.9", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "metaheuristics; tabu search; timetabling", } @Article{Salmela:2006:MSM, author = "Leena Salmela and Jorma Tarhio and Jari Kyt{\"o}joki", title = "Multipattern string matching with $q$-grams", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "1.1:1--1.1:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1187438", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present three algorithms for exact string matching of multiple patterns. Our algorithms are filtering methods, which apply $q$-grams and bit parallelism. We ran extensive experiments with them and compared them with various versions of earlier algorithms, e.g., different trie implementations of the Aho--Corasick algorithm. All of our algorithms appeared to be substantially faster than earlier solutions for sets of 1,000--10,000 patterns and the good performance of two of them continues to 100,000 patterns. The gain is because of the improved filtering efficiency caused by $q$-grams.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "content scanning; intrusion detection; multiple string matching", } @Article{Sinha:2006:CES, author = "Ranjan Sinha and Justin Zobel and David Ring", title = "Cache-efficient string sorting using copying", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "1.2:1--1.2:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1187439", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Burstsort is a cache-oriented sorting technique that uses a dynamic trie to efficiently divide large sets of string keys into related subsets small enough to sort in cache. In our original burstsort, string keys sharing a common prefix were managed via a bucket of pointers represented as a list or array; this approach was found to be up to twice as fast as the previous best string sorts, mostly because of a sharp reduction in out-of-cache references. In this paper, we introduce C-burstsort, which copies the unexamined tail of each key to the bucket and discards the original key to improve data locality. On both Intel and PowerPC architectures, and on a wide range of string types, we show that sorting is typically twice as fast as our original burstsort and four to five times faster than multikey quicksort and previous radixsorts. A variant that copies both suffixes and record pointers to buckets, CP-burstsort, uses more memory, but provides stable sorting. In current computers, where performance is limited by memory access latencies, these new algorithms can dramatically reduce the time needed for internal sorting of large numbers of strings.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; cache; experimental algorithms; sorting; string management; tries", } @Article{Penner:2006:CFI, author = "Michael Penner and Viktor K. Prasanna", title = "Cache-Friendly implementations of transitive closure", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "1.3:1--1.3:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1210586", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The topic of cache performance has been well studied in recent years. Compiler optimizations exist and optimizations have been done for many problems. Much of this work has focused on dense linear algebra problems. At first glance, the Floyd--Warshall algorithm appears to fall into this category. In this paper, we begin by applying two standard cache-friendly optimizations to the Floyd--Warshall algorithm and show limited performance improvements. We then discuss the unidirectional space time representation (USTR). We show analytically that the USTR can be used to reduce the amount of processor-memory traffic by a factor of $O(\sqrt C)$, where $C$ is the cache size, for a large class of algorithms. Since the USTR leads to a tiled implementation, we develop a tile size selection heuristic to intelligently narrow the search space for the tile size that minimizes total execution time. Using the USTR, we develop a cache-friendly implementation of the Floyd--Warshall algorithm. We show experimentally that this implementation minimizes the level-1 and level-2 cache misses and TLB misses and, therefore, exhibits the best overall performance. Using this implementation, we show a $2 \times$ improvement in performance over the best compiler optimized implementation on three different architectures. Finally, we show analytically that our implementation of the Floyd--Warshall algorithm is asymptotically optimal with respect to processor-memory traffic. We show experimental results for the Pentium III, Alpha, and MIPS R12000 machines using problem sizes between 1024 and 2048 vertices. We demonstrate improved cache performance using the Simplescalar simulator.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "data structures; Floyd--Warshall algorithm; systolic array algorithms", } @Article{Goshi:2006:ADM, author = "Justin Goshi and Richard E. Ladner", title = "Algorithms for dynamic multicast key distribution", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "1.4:1--1.4:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1210587", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study the problem of multicast key distribution for group security. Secure group communication systems typically rely on a group key, which is a secret shared among the members of the group. This key is used to provide privacy by encrypting all group communications. Because groups can be large and highly dynamic, it becomes necessary to change the group key in a scalable and secure fashion when members join and leave the group. We present a series of algorithms for solving this problem based on key trees. The algorithms attempt to minimize the worst-case communication cost of updates by maintaining balanced key tree structures. We focus on the trade-off between the communication cost because of the structure of the tree and that due to the overhead of restructuring the tree to maintain its balanced structure. The algorithms are analyzed for worst-case tree structure bounds and evaluated empirically via simulations.", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dynamic key distribution; experimental algorithms; multicast", } @Article{Aleksandrov:2006:PPG, author = "Lyudmil Aleksandrov and Hristo Djidjev and Hua Guo and Anil Maheshwari", title = "Partitioning planar graphs with costs and weights", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "1.5:1--1.5:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1210588", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A graph separator is a set of vertices or edges whose removal divides an input graph into components of bounded size. This paper describes new algorithms for computing separators in planar graphs as well as techniques that can be used to speed up the implementation of graph partitioning algorithms and improve the partition quality. In particular, we consider planar graphs with costs and weights on the vertices, where weights are used to estimate the sizes of the partitions and costs are used to estimate the size of the separator. We show that in these graphs one can always find a small cost separator (consisting of vertices or edges) that partitions the graph into components of bounded weight. We describe implementations of the partitioning algorithms and discuss results of our experiments.", acknowledgement = ack-nhfb, articleno = "1.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "graph algorithms; graph partitioning algorithms; graph separators; implementation", } @Article{Ilinkin:2006:HEC, author = "Ivayio Ilinkin and Ravi Janardan and Michiel Smid and Eric Johnson and Paul Castillo and J{\"o}rg Schwerdt", title = "Heuristics for estimating contact area of supports in layered manufacturing", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "1.6:1--1.6:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1210589", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Layered manufacturing is a technology that allows physical prototypes of three-dimensional(3D) models to be built directly from their digital representation, as a stack of two-dimensional(2D) layers. A key design problem here is the choice of a suitable direction in which the digital model should be oriented and built so as to minimize the area of contact between the prototype and temporary support structures that are generated during the build. Devising an efficient algorithm for computing such a direction has remained a difficult problem for quite some time. In this paper, a suite of efficient and practical heuristics is presented for estimating the minimum contact area. Also given is a technique for evaluating the quality of the estimate provided by any heuristic, which does not require knowledge of the (unknown and hard-to-compute) optimal solution; instead, it provides an indirect upper bound on the quality of the estimate via two relatively easy-to-compute quantities. The algorithms are based on various techniques from computational geometry, such as ray-shooting, convex hulls, boolean operations on polygons, and spherical arrangements, and have been implemented and tested. Experimental results on a wide range of real-world models show that the heuristics perform quite well in practice.", acknowledgement = ack-nhfb, articleno = "1.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithm implementation and testing; computational geometry", } @Article{Pearce:2006:DTS, author = "David J. Pearce and Paul H. J. Kelly", title = "A dynamic topological sort algorithm for directed acyclic graphs", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "1.7:1--1.7:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1210590", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider the problem of maintaining the topological order of a directed acyclic graph (DAG) in the presence of edge insertions and deletions. We present a new algorithm and, although this has inferior time complexity compared with the best previously known result, we find that its simplicity leads to better performance in practice. In addition, we provide an empirical comparison against the three main alternatives over a large number of random DAGs. The results show our algorithm is the best for sparse digraphs and only a constant factor slower than the best on dense digraphs.", acknowledgement = ack-nhfb, articleno = "1.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dynamic graph algorithms; topological sort", } @Article{Flammini:2006:RAF, author = "Michele Flammini and Alfredo Navarra and Stephane Perennes", title = "The ``real'' approximation factor of the {MST} heuristic for the minimum energy broadcasting", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.10:1--2.10:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216587", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "This paper deals with one of the most studied problems in the last few years in the field of wireless communication in ad-hoc networks. The problem consists of reducing the total energy consumption of wireless radio stations distributed over a given area of interest in order to perform the basic pattern of communication by a broadcast. Recently, a tight 6-approximation of the minimum spanning tree heuristic has been proven. While such a bound is theoretically optimal if compared to the known lower bound of 6, there is an obvious gap with practical experimental results. By extensive experiments, proposing a new technique to generate input instances and supported by theoretical results, we show how the approximation ratio can be actually considered close to 4 for a ``real-world'' set of instances. We consider, in fact, instances more representative of common practices. Those are usually composed by considerable number of nodes uniformly and randomly distributed inside the area of interest.", acknowledgement = ack-nhfb, articleno = "2.10", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "ad-hoc networks; broadcast; energy saving; spanning tree", } @Article{Nikoletseas:2006:JSS, author = "Sotiris Nikoletseas", title = "{JEA Special Section}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.1:1--2.1:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216578", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Fahle:2006:FBB, author = "Torsten Fahle and Karsten Tiemann", title = "A faster branch-and-bound algorithm for the test-cover problem based on set-covering techniques", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.2:1--2.2:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216579", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The test-cover problem asks for the minimal number of tests needed to uniquely identify a disease, infection, etc. A collection of branch-and-bound algorithms was proposed by De Bontridder et al. [2002]. Based on their work, we introduce several improvements that are compatible with all techniques described in De Bontridder et al. [2002] and the more general setting of {\em weighted\/} test-cover problems. We present a faster data structure, cost-based variable fixing, and adapt well-known set-covering techniques, including Lagrangian relaxation and upper-bound heuristics. The resulting algorithm solves benchmark instances up to 10 times faster than the former approach and up to 100 times faster than a general MIP solver.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "branch-and-bound; Lagrangian relaxation; set-cover problem; test-cover problem; variable fixing", } @Article{Leone:2006:FPN, author = "Pierre Leone and Jose Rolim and Paul Albuquerque and Christian Mazza", title = "A framework for probabilistic numerical evaluation of sensor networks: a case study of a localization protocol", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.3:1--2.3:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216580", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper we show how to use stochastic estimation methods to investigate topological properties of sensor networks as well as the behavior of dynamical processes on these networks. The framework is particularly important to study problems for which no theoretical results are known, or cannot be directly applied in practice, for instance, when only asymptotic results are available. We also interpret Russo's formula in the context of sensor networks and thus obtain practical information on their reliability. As a case study, we analyze a localization protocol for wireless sensor networks and validate our approach by numerical experiments. Finally, we mention three applications of our approach: estimating the number of pivotal sensors in a real network, minimizing the number of such sensors for robustness purposes during the network design and estimating the distance between successive localized positions for mobile sensor networks.", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "localization process and reliability; sensor networks; stochastic recursive estimation", } @Article{Festa:2006:GPR, author = "Paola Festa and Panos M. Pardalos and Leonidas S. Pitsoulis and Mauricio G. C. Resende", title = "{GRASP} with path relinking for the weighted {MAXSAT} problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.4:1--2.4:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216581", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A GRASP with path relinking for finding good-quality solutions of the weighted maximum satisfiability problem (MAX-SAT) is described in this paper. GRASP, or Greedy Randomized Adaptive Search Procedure, is a randomized multistart metaheuristic, where, at each iteration, locally optimal solutions are constructed, each independent of the others. Previous experimental results indicate its effectiveness for solving weighted MAX-SAT instances. Path relinking is a procedure used to intensify the search around good-quality isolated solutions that have been produced by the GRASP heuristic. Experimental comparison of the pure GRASP (without path relinking) and the GRASP with path relinking illustrates the effectiveness of path relinking in decreasing the average time needed to find a good-quality solution for the weighted maximum satisfiability problem.", acknowledgement = ack-nhfb, articleno = "2.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; experimentation; GRASP; heuristics; path relinking; performance; time-to-target plots", } @Article{Mehlhorn:2006:IMC, author = "Kurt Mehlhorn and Dimitrios Michail", title = "Implementing minimum cycle basis algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.5:1--2.5:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216582", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this paper, we consider the problem of computing a minimum cycle basis of an undirected graph $G$ = ($V$, $E$) with $n$ vertices and $m$ edges. We describe an efficient implementation of an $O(m^3 + mn^2 \log n)$ algorithm. For sparse graphs, this is the currently best-known algorithm. This algorithm's running time can be partitioned into two parts with time $O(m^3)$ and $O(m^2 n + mn^2 \log n)$, respectively. Our experimental findings imply that for random graphs the true bottleneck of a sophisticated implementation is the $O(m^2 n + mn^2 \log n)$ part. A straightforward implementation would require $\Omega(n m)$ shortest-path computations. Thus, we develop several heuristics in order to get a practical algorithm. Our experiments show that in random graphs our techniques result in a significant speed-up. Based on our experimental observations, we combine the two fundamentally different approaches to compute a minimum cycle basis to obtain a new hybrid algorithm with running time $O(m^2 n^2)$. The hybrid algorithm is very efficient, in practice, for random dense unweighted graphs. Finally, we compare these two algorithms with a number of previous implementations for finding a minimum cycle basis of an undirected graph.", acknowledgement = ack-nhfb, articleno = "2.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "cycle basis; graph algorithms", } @Article{Heinrich-Litan:2006:RCR, author = "Laura Heinrich-Litan and Marco E. L{\"u}bbecke", title = "Rectangle covers revisited computationally", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.6:1--2.6:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216583", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider the problem of covering an orthogonal polygon with a minimum number of axis-parallel rectangles from a computational point of view. We propose an integer program which is the first general approach to obtain provably optimal solutions to this well-studied NP-hard problem. It applies to common variants like covering only the corners or the boundary of the polygon and also to the weighted case. In experiments, it turns out that the linear programming relaxation is extremely tight and rounding a fractional solution is an immediate high-quality heuristic. We obtain excellent experimental results for polygons originating from VLSI design, fax data sheets, black and white images, and for random instances. Making use of the dual linear program, we propose a stronger lower bound on the optimum, namely, the cardinality of a fractional stable set. Furthermore, we outline ideas how to make use of this bound in primal--dual-based algorithms. We give partial results, which make us believe that our proposals have a strong potential to settle the main open problem in the area: To find a constant factor approximation algorithm for the rectangle cover problem.", acknowledgement = ack-nhfb, articleno = "2.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "integer programming; linear programming", } @Article{Panagopoulou:2006:APN, author = "Panagiota N. Panagopoulou and Paul G. Spirakis", title = "Algorithms for pure {Nash} equilibria in weighted congestion games", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.7:1--2.7:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216584", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In large-scale or evolving networks, such as the Internet, there is no authority possible to enforce a centralized traffic management. In such situations, game theory, and especially the concepts of Nash equilibria and congestion games [Rosenthal 1973] are a suitable framework for analyzing the equilibrium effects of selfish routes selection to network delays. We focus here on {\em single-commodity\/} networks where selfish users select paths to route their loads (represented by arbitrary integer {\em weights\/}). We assume that individual link delays are equal to the total load of the link. We then focus on the algorithm suggested in Fotakis et al. [2005], i.e., a potential-based method for finding {\em pure\/} Nash equilibria in such networks. A superficial analysis of this algorithm gives an upper bound on its time, which is polynomial in $n$ (the number of users) and the sum of their weights $W$. This bound can be exponential in $n$ when some weights are exponential. We provide strong experimental evidence that this algorithm actually converges to a pure Nash equilibrium in {\em polynomial time}. More specifically, our experimental findings suggest that the running time is a polynomial function of $n$ and $\log W$. In addition, we propose an initial allocation of users to paths that dramatically accelerates this algorithm, compared to an arbitrary initial allocation. A by-product of our research is the discovery of a weighted potential function when link delays are {\em exponential\/} to their loads. This asserts the existence of pure Nash equilibria for these delay functions and extends the result of Fotakis et al. [2005].", acknowledgement = ack-nhfb, articleno = "2.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "congestion games; game theory; pure Nash equilibria", } @Article{Mohring:2006:PGS, author = "Rolf H. M{\"o}hring and Heiko Schilling and Birk Sch{\"u}tz and Dorothea Wagner and Thomas Willhalm", title = "Partitioning graphs to speedup {Dijkstra}'s algorithm", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.8:1--2.8:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216585", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study an acceleration method for point-to-point shortest-path computations in large and sparse directed graphs with given nonnegative arc weights. The acceleration method is called the {\em arc-flag approach\/} and is based on Dijkstra's algorithm. In the arc-flag approach, we allow a preprocessing of the network data to generate additional information, which is then used to speedup shortest-path queries. In the preprocessing phase, the graph is divided into regions and information is gathered on whether an arc is on a shortest path into a given region. The arc-flag method combined with an appropriate partitioning and a bidirected search achieves an average speedup factor of more than 500 compared to the standard algorithm of Dijkstra on large networks (1 million nodes, 2.5 million arcs). This combination narrows down the search space of Dijkstra's algorithm to almost the size of the corresponding shortest path for long-distance shortest-path queries. We conduct an experimental study that evaluates which partitionings are best suited for the arc-flag method. In particular, we examine partitioning algorithms from computational geometry and a multiway arc separator partitioning. The evaluation was done on German road networks. The impact of different partitions on the speedup of the shortest path algorithm are compared. Furthermore, we present an extension of the speedup technique to multiple levels of partitions. With this multilevel variant, the same speedup factors can be achieved with smaller space requirements. It can, therefore, be seen as a compression of the precomputed data that preserves the correctness of the computed shortest paths.", acknowledgement = ack-nhfb, articleno = "2.8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "acceleration method; Dijkstra's algorithm; road network; shortest path", } @Article{Boukerche:2006:ICC, author = "Azzedine Boukerche and Alba Cristina Magalhaes {Alves De Melo}", title = "Integrating coordinated checkpointing and recovery mechanisms into {DSM} synchronization barriers", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "11", pages = "2.9:1--2.9:??", month = "????", year = "2006", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1187436.1216586", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:06:20 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Distributed shared memory (DSM) creates an abstraction of a physical shared memory that parallel programmers can access. Most recent software DSM systems provide relaxed-memory models that guarantee consistency only at synchronization operations, such as locks and barriers. As the main goal of DSM systems is to provide support for long-term computation-intensive applications, checkpointing and recovery mechanisms are highly desirable. This article presents and evaluates the integration of a coordinated checkpointing mechanism to the barrier primitive that is usually provided with many DSM systems. Our results on some popular benchmarks and a real parallel application show that the overhead introduced during the failure-free execution is often small.", acknowledgement = ack-nhfb, articleno = "2.9", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "barrier synchronization; distributed shared memory", } @Article{Anonymous:2008:EGC, author = "Anonymous", title = "Engineering graph clustering: {Models} and experimental evaluation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.1:1--1.1:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1227162", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A promising approach to graph clustering is based on the intuitive notion of intracluster density versus intercluster sparsity. As for the weighted case, clusters should accumulate lots of weight, in contrast to their connection to the remaining graph, which should be light. While both formalizations and algorithms focusing on particular aspects of this rather vague concept have been proposed, no conclusive argument on their appropriateness has been given. In order to deepen the understanding of particular concepts, including both quality assessment as well as designing new algorithms, we conducted an experimental evaluation of graph-clustering approaches. By combining proved techniques from graph partitioning and geometric clustering, we also introduce a new approach that compares favorably.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "clustering algorithms; experimental evaluation; graph clustering; quality measures", } @Article{Barsky:2008:GAT, author = "Marina Barsky and Ulrike Stege and Alex Thomo and Chris Upton", title = "A graph approach to the threshold all-against-all substring matching problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.10:1--1.10:??", month = jun, year = "2008", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1370596.1370601", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present a novel graph model and an efficient algorithm for solving the ``threshold all against all'' problem, which involves searching two strings (with length $M$ and $N$, respectively) for all maximal approximate substring matches of length at least $S$, with up to $K$ differences. Our algorithm solves the problem in time $O(MNK_3)$, which is a considerable improvement over the previous known bound for this problem. We also provide experimental evidence that, in practice, our algorithm exhibits a better performance than its worst-case running time.", acknowledgement = ack-nhfb, articleno = "1.10", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "bioinformatics; complexity; string matching", } @Article{Dietzfelbinger:2008:DIB, author = "Martin Dietzfelbinger and Martin H{\"u}hne and Christoph Weidling", title = "A dictionary implementation based on dynamic perfect hashing", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.11:1--1.11:??", month = jun, year = "2008", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1370596.1370602", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We describe experimental results on an implementation of a dynamic dictionary. The basis of our implementation is ``dynamic perfect hashing'' as described by Dietzfelbinger et al. ({\em SIAM J. Computing 23}, 1994, pp. 738--761), an extension of the storage scheme proposed by Fredman et al. ({\em J. ACM\/} 31, 1984, pp. 538--544). At the top level, a hash function is used to partition the keys to be stored into several sets. On the second level, there is a perfect hash function for each of these sets. This technique guarantees $O(1)$ worst-case time for lookup and expected $O(1)$ amortized time for insertion and deletion, while only linear space is required. We study the practical performance of dynamic perfect hashing and describe improvements of the basic scheme. The focus is on the choice of the hash function (both for integer and string keys), on the efficiency of rehashing, on the handling of small buckets, and on the space requirements of the implementation.", acknowledgement = ack-nhfb, articleno = "1.11", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "data structures; dictionaries; dynamic hashing; hash functions; implementation", } @Article{Maniscalco:2008:EVA, author = "Michael A. Maniscalco and Simon J. Puglisi", title = "An efficient, versatile approach to suffix sorting", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.2:1--1.2:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1278374", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Sorting the suffixes of a string into lexicographical order is a fundamental task in a number of contexts, most notably lossless compression (Burrows--Wheeler transformation) and text indexing (suffix arrays). Most approaches to suffix sorting produce a sorted array of suffixes directly, continually moving suffixes into their final place in the array until the ordering is complete. In this article, we describe a novel and resource-efficient (time and memory) approach to suffix sorting, which works in a complementary way --- by assigning each suffix its rank in the final ordering, before converting to a sorted array, if necessary, once all suffixes are ranked. We layer several powerful extensions on this basic idea and show experimentally that our approach is superior to other leading algorithms in a variety of real-world contexts.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "Burrows--Wheeler transform; suffix array; suffix sorting; suffix tree", } @Article{Aloul:2008:SBP, author = "Fadi A. Aloul and Arathi Ramani and Igor L. Markov and Karem A. Sakallah", title = "Symmetry breaking for pseudo-{Boolean} formulas", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.3:1--1.3:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1278375", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Many important tasks in design automation and artificial intelligence can be performed in practice via reductions to Boolean satisfiability (SAT). However, such reductions often omit application-specific structure, thus handicapping tools in their competition with creative engineers. Successful attempts to represent and utilize additional structure on Boolean variables include recent work on 0-1 integer linear programming (ILP) and symmetries in SAT. Those extensions gracefully accommodate well-known advances in SAT solving, however, no previous work has attempted to combine both extensions. Our work shows (i) how one can detect and use symmetries in instances of 0-1 ILP, and (ii) what benefits this may bring.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "graph automorphism", } @Article{Pellegrini:2008:EIT, author = "Marco Pellegrini and Giordano Fusco", title = "Efficient {IP} table lookup via adaptive stratified trees with selective reconstructions", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.4:1--1.4:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1278376", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "IP address lookup is a critical operation for high-bandwidth routers in packet-switching networks, such as Internet. The lookup is a nontrivial operation, since it requires searching for the longest prefix, among those stored in a (large) given table, matching the IP address. Ever increasing routing table size, traffic volume, and links speed demand new and more efficient algorithms. Moreover, the imminent move to IPv6 128-bit addresses will soon require a rethinking of previous technical choices. This article describes a the new data structure for solving the IP table lookup problem christened the adaptive stratified tree (AST). The proposed solution is based on casting the problem in geometric terms and on repeated application of efficient local geometric optimization routines. Experiments with this approach have shown that in terms of storage, query time, and update time the AST is at a par with state of the art algorithms based on data compression or string manipulations (and often it is better on some of the measured quantities).", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "data structures; IP table lookup", } @Article{Navarro:2008:DSA, author = "Gonzalo Navarro and Nora Reyes", title = "Dynamic spatial approximation trees", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.5:1--1.5:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1322337", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Metric space searching is an emerging technique to address the problem of efficient similarity searching in many applications, including multimedia databases and other repositories handling complex objects. Although promising, the metric space approach is still immature in several aspects that are well established in traditional databases. In particular, most indexing schemes are static, that is, few of them tolerate insertion or deletion of elements at reasonable cost over an existing index. The spatial approximation tree ({\em sa--tree\/}) has been experimentally shown to provide a good tradeoff between construction cost, search cost, and space requirement. However, the {\em sa--tree\/} is static, which renders it unsuitable for many database applications. In this paper, we study different methods to handle insertions and deletions on the {\em sa--tree\/} at low cost. In many cases, the dynamic construction (by successive insertions) is even faster than the previous static construction, and both are similar elsewhere. In addition, the dynamic version significantly improves the search performance of {\em sa--trees\/} in virtually all cases. The result is a much more practical data structure that can be useful in a wide range of database applications.", acknowledgement = ack-nhfb, articleno = "1.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "multimedia databases; similarity or proximity search; spatial and multidimensional search; spatial approximation tree", } @Article{Li:2008:EAC, author = "Keqin Li", title = "Experimental average-case performance evaluation of online algorithms for routing and wavelength assignment and throughput maximization in {WDM} optical networks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.7:1--1.7:??", month = jun, year = "2008", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1370596.1370598", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We investigate the problem of online routing and wavelength assignment and the related throughput maximization problem in wavelength division multiplexing optical networks. It is pointed out that these problems are highly inapproximable, that is, the competitive ratio of any algorithm is at least a polynomial. We evaluate the average-case performance of several online algorithms, which have no knowledge of future arriving connection requests when processing the current connection request. Our experimental results on a wide range of optical networks demonstrate that the average-case performance of these algorithms are very close to optimal.", acknowledgement = ack-nhfb, articleno = "1.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "average-case performance; competitive ratio; online algorithm; optical network; routing; wavelength assignment; wavelength division multiplexing", } @Article{Biggar:2008:ESS, author = "Paul Biggar and Nicholas Nash and Kevin Williams and David Gregg", title = "An experimental study of sorting and branch prediction", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.8:1--1.8:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1370599", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Sorting is one of the most important and well-studied problems in computer science. Many good algorithms are known which offer various trade-offs in efficiency, simplicity, memory use, and other factors. However, these algorithms do not take into account features of modern computer architectures that significantly influence performance. Caches and branch predictors are two such features and, while there has been a significant amount of research into the cache performance of general purpose sorting algorithms, there has been little research on their branch prediction properties. In this paper, we empirically examine the behavior of the branches in all the most common sorting algorithms. We also consider the interaction of cache optimization on the predictability of the branches in these algorithms. We find insertion sort to have the fewest branch mispredictions of any comparison-based sorting algorithm, that bubble and shaker sort operate in a fashion that makes their branches highly unpredictable, that the unpredictability of shellsort's branches improves its caching behavior, and that several cache optimizations have little effect on mergesort's branch mispredictions. We find also that optimizations to quicksort, for example the choice of pivot, have a strong influence on the predictability of its branches. We point out a simple way of removing branch instructions from a classic heapsort implementation and also show that unrolling a loop in a cache-optimized heapsort implementation improves the predicitability of its branches. Finally, we note that when sorting random data two-level adaptive branch predictors are usually no better than simpler bimodal predictors. This is despite the fact that two-level adaptive predictors are almost always superior to bimodal predictors, in general.", acknowledgement = ack-nhfb, articleno = "1.8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "branch prediction; caching; pipeline architectures; sorting", } @Article{Hazel:2008:TCL, author = "Thomas Hazel and Laura Toma and Jan Vahrenhold and Rajiv Wickremesinghe", title = "Terracost: {Computing} least-cost-path surfaces for massive grid terrains", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "1.9:1--1.9:??", month = jun, year = "2008", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1370596.1370600", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "This paper addresses the problem of computing least-cost-path surfaces for massive grid terrains. Consider a grid terrain $T$ and let $C$ be a cost grid for $T$ such that every point in $C$ stores a value that represents the cost of traversing the corresponding point in $T$. Given $C$ and a set of sources $S \in T$, a least-cost-path grid $\Delta$ for $T$ is a grid such that every point in $\Delta$ represents the distance to the source in $S$ that can be reached with minimal cost. We present a scalable approach to computing least-cost-path grids. Our algorithm, terracost, is derived from our previous work on I/O-efficient shortest paths on grids and uses $O(\hbox{sort}(n))$ I/Os, where $\hbox{sort}(n)$ is the complexity of sorting $n$ items of data in the I/O-model of Aggarwal and Vitter. We present the design, the analysis, and an experimental study of terracost. An added benefit of the algorithm underlying terracost is that it naturally lends itself to parallelization. We have implemented terracost in a distributed environment using our cluster management tool and report on experiments that show that it obtains speedup near-linear with the size of the cluster. To the best of our knowledge, this is the first experimental evaluation of a multiple-source least-cost-path algorithm in the external memory setting.", acknowledgement = ack-nhfb, articleno = "1.9", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "data structures and algorithms; Dijkstra's algorithm; I/O-efficiency; shortest paths; terrain data", } @Article{Arge:2008:P, author = "Lars Arge and Giuseppe F. Italiano", title = "Preface", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "2.1:1--2.1:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1227163", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Brodal:2008:ECO, author = "Gerth St{\o}lting Brodal and Rolf Fagerberg and Kristoffer Vinther", title = "Engineering a cache-oblivious sorting algorithm", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "2.2:1--2.2:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1227164", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "This paper is an algorithmic engineering study of cache-oblivious sorting. We investigate by empirical methods a number of implementation issues and parameter choices for the cache-oblivious sorting algorithm Lazy Funnelsort and compare the final algorithm with Quicksort, the established standard for comparison-based sorting, as well as with recent cache-aware proposals. The main result is a carefully implemented cache-oblivious sorting algorithm, which, our experiments show, can be faster than the best Quicksort implementation we are able to find for input sizes well within the limits of RAM. It is also at least as fast as the recent cache-aware implementations included in the test. On disk, the difference is even more pronounced regarding Quicksort and the cache-aware algorithms, whereas the algorithm is slower than a careful implementation of multiway Mergesort, such as TPIE.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "cache-oblivious algorithms; funnelsort; quicksort", } @Article{Bender:2008:SSH, author = "Michael A. Bender and Bryan Bradley and Geetha Jagannathan and Krishnan Pillaipakkamnatt", title = "Sum-of-squares heuristics for bin packing and memory allocation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "2.3:1--2.3:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1227165", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The sum-of-squares algorithm (SS) was introduced by Csirik, Johnson, Kenyon, Shor, and Weber for online bin packing of integral-sized items into integral-sized bins. First, we show the results of experiments from two new variants of the SS algorithm. The first variant, which runs in time $O(n \sqrt{B \log B})$, appears to have almost identical expected waste as the sum-of-squares algorithm on all the distributions mentioned in the original papers on this topic. The other variant, which runs in $O(n \log B)$ time, performs well on most, but not on all of those distributions. We also apply SS to the online memory-allocation problem. Our experimental comparisons between SS and Best Fit indicate that neither algorithm is consistently better than the other. If the amount of randomness in item sizes is low, SS appears to have lower waste than Best Fit, whereas, if the amount of randomness is high Best Fit appears to have lower waste than SS. Our experiments suggest that in both real and synthetic traces, SS does not seem to have an asymptotic advantage over Best Fit, in contrast with the bin-packing problem.", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "bin packing; memory allocation; sum of squares", } @Article{Pyrga:2008:EMT, author = "Evangelia Pyrga and Frank Schulz and Dorothea Wagner and Christos Zaroliagis", title = "Efficient models for timetable information in public transportation systems", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "2.4:1--2.4:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1227166", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider two approaches that model timetable information in public transportation systems as shortest-path problems in weighted graphs. In the {\em time-expanded\/} approach, every event at a station, e.g., the departure of a train, is modeled as a node in the graph, while in the {\em time-dependent\/} approach the graph contains only one node per station. Both approaches have been recently considered for (a simplified version of) the earliest arrival problem, but little is known about their relative performance. Thus far, there are only theoretical arguments in favor of the time-dependent approach. In this paper, we provide the first extensive experimental comparison of the two approaches. Using several real-world data sets, we evaluate the performance of the basic models and of several new extensions towards realistic modeling. Furthermore, new insights on solving bicriteria optimization problems in both models are presented. The time-expanded approach turns out to be more robust for modeling more complex scenarios, whereas the time-dependent approach shows a clearly better performance.", acknowledgement = ack-nhfb, articleno = "2.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "itinerary query; public transportation system; shortest path; timetable information", } @Article{Leaver-Fay:2008:FPH, author = "Andrew Leaver-Fay and Yuanxin Liu and Jack Snoeyink and Xueyi Wang", title = "Faster placement of hydrogens in protein structures by dynamic programming", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "2.5:1--2.5:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1227167", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "M. Word and coauthors from the Richardsons' 3D Protein Structure laboratory at Duke University propose {\em dot scores\/} to measure interatomic interactions in molecular structures. Their program REDUCE uses these scores in a brute-force search to solve instances of the {\em NP\/}-hard problem of finding the optimal placement of hydrogen atoms in molecular structures determined by X-ray crystallography. We capture the central combinatorial optimization in the hydrogen placement problem with an abstraction that we call an interaction (hyper)graph. REDUCE's dot-based scoring function cannot be decomposed into the sum of pair interactions, but because the function is short ranged we are able to decompose it into the sum of single, pair, triple, and quadruple interactions that we represent by graph hyperedges. Almost every interaction graph we have observed has had a small treewidth. This fact allows us to replace the brute-force search by dynamic programming, giving speedups of nearly ten orders of magnitude. This dynamic programming has been incorporated into REDUCE and is available for download.", acknowledgement = ack-nhfb, articleno = "2.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dynamic programming; hard-sphere model; hydrogen bonds; hydrogen placement; protein structure; treewidth", } @Article{Demetrescu:2008:PA, author = "Camil Demetrescu and Roberto Tamassia", title = "Papers from {ALENEX 2005}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "3.1:1--3.1:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1402293", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "3.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Brodal:2008:AQ, author = "Gerth St{\o}lting Brodal and Rolf Fagerberg and Gabriel Moruz", title = "On the adaptiveness of {Quicksort}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "3.2:1--3.2:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1402294", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Quicksort was first introduced in 1961 by Hoare. Many variants have been developed, the best of which are among the fastest generic-sorting algorithms available, as testified by the choice of Quicksort as the default sorting algorithm in most programming libraries. Some sorting algorithms are adaptive, i.e., they have a complexity analysis that is better for inputs, which are nearly sorted, according to some specified measure of presortedness. Quicksort is not among these, as it uses $\Omega (n \log n)$ comparisons even for sorted inputs. However, in this paper, we demonstrate empirically that the actual running time of Quicksort {\em is\/} adaptive with respect to the presortedness measure Inv. Differences close to a factor of two are observed between instances with low and high Inv value. We then show that for the randomized version of Quicksort, the number of element {\em swaps\/} performed is {\em provably\/} adaptive with respect to the measure $\hbox{Inv}$. More precisely, we prove that randomized Quicksort performs expected $O(n (1 + \log(1 + \hbox{Inv} / n)))$ element swaps, where $\hbox{Inv}$ denotes the number of inversions in the input sequence. This result provides a theoretical explanation for the observed behavior and gives new insights on the behavior of Quicksort. We also give some empirical results on the adaptive behavior of Heapsort and Mergesort.", acknowledgement = ack-nhfb, articleno = "3.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "adaptive sorting; branch mispredictions; Quicksort", } @Article{Codenotti:2008:ESD, author = "Bruno Codenotti and Benton Mccune and Sriram Pemmaraju and Rajiv Raman and Kasturi Varadarajan", title = "An experimental study of different approaches to solve the market equilibrium problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "3.3:1--3.3:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1402295", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Over the last few years, the problem of computing market equilibrium prices for exchange economies has received much attention in the theoretical computer science community. Such activity led to a flurry of polynomial time algorithms for various restricted, yet significant, settings. The most important restrictions arise either when the traders' utility functions satisfy a property known as {\em gross substitutability\/} or when the initial endowments are proportional (the Fisher model). In this paper, we experimentally compare the performance of some of these recent algorithms against that of the most used software packages. In particular, we evaluate the following approaches: (1) the solver PATH, available under GAMS/MPSGE, a popular tool for computing market equilibrium prices; (2) a discrete version of a simple iterative price update scheme called t{\^a}tonnement; (3) a discrete version of the welfare adjustment process; (4) convex feasibility programs that characterize the equilibrium in some special cases. We analyze the performance of these approaches on models of exchange economies where the consumers are equipped with utility functions, which are widely used in real world applications. The outcomes of our experiments consistently show that many market settings allow for an efficient computation of the equilibrium, well beyond the restrictions under which the theory provides polynomial time guarantees. For some of the approaches, we also identify models where they are prone to failure.", acknowledgement = ack-nhfb, articleno = "3.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "market equilibrium", } @Article{Dementiev:2008:BEM, author = "Roman Dementiev and Juha K{\"a}rkk{\"a}inen and Jens Mehnert and Peter Sanders", title = "Better external memory suffix array construction", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "3.4:1--3.4:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1402296", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Suffix arrays are a simple and powerful data structure for text processing that can be used for full text indexes, data compression, and many other applications, in particular, in bioinformatics. However, so far, it has appeared prohibitive to build suffix arrays for huge inputs that do not fit into main memory. This paper presents design, analysis, implementation, and experimental evaluation of several new and improved algorithms for suffix array construction. The algorithms are asymptotically optimal in the worst case or on average. Our implementation can construct suffix arrays for inputs of up to 4-GB in hours on a low-cost machine. As a tool of possible independent interest, we present a systematic way to design, analyze, and implement {\em pipelined\/} algorithms.", acknowledgement = ack-nhfb, articleno = "3.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithm engineering; algorithms for strings; external memory; I/O-efficient; large data sets; secondary memory; suffix array", } @Article{Swenson:2008:ATE, author = "Krister M. Swenson and Mark Marron and Joel V. Earnest-Deyoung and Bernard M. E. Moret", title = "Approximating the true evolutionary distance between two genomes", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "3.5:1--3.5:??", month = jun, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1227161.1402297", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "As more and more genomes are sequenced, evolutionary biologists are becoming increasingly interested in evolution at the level of whole genomes, in scenarios in which the genome evolves through insertions, duplications, deletions, and movements of genes along its chromosomes. In the mathematical model pioneered by Sankoff and others, a unichromosomal genome is represented by a signed permutation of a multiset of genes; Hannenhalli and Pevzner showed that the edit distance between two signed permutations of the same set can be computed in polynomial time when all operations are inversions. El-Mabrouk extended that result to allow deletions and a limited form of insertions (which forbids duplications); in turn we extended it to compute a nearly optimal edit sequence between an arbitrary genome and the identity permutation. In this paper we generalize our approach to compute distances between two arbitrary genomes, but focus on approximating the true evolutionary distance rather than the edit distance. We present experimental results showing that our algorithm produces excellent estimates of the true evolutionary distance up to a (high) threshold of saturation; indeed, the distances thus produced are good enough to enable the simple neighbor-joining procedure to reconstruct our test trees with high accuracy.", acknowledgement = ack-nhfb, articleno = "3.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "duplications; evolution; inversions; pairwise distances; whole-genome data", } @Article{Krommidas:2008:ESA, author = "Ioannis Krommidas and Christos Zaroliagis", title = "An experimental study of algorithms for fully dynamic transitive closure", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "12", pages = "16:1--16:??", month = jun, year = "2008", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1370596.1370597", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:17:58 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We have conducted an extensive experimental study on algorithms for fully dynamic transitive closure. We have implemented the recent fully dynamic algorithms by King [1999], Roditty [2003], Roditty and Zwick [2002, 2004], and Demetrescu and Italiano [2000, 2005] along with several variants and compared them to pseudo fully dynamic and simple-minded algorithms developed in a previous study [Frigioni et al. 2001]. We tested and compared these implementations on random inputs, synthetic (worst-case) inputs, and on inputs motivated by real-world graphs. Our experiments reveal that some of the dynamic algorithms can really be of practical value in many situations.", acknowledgement = ack-nhfb, articleno = "16", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "dynamic algorithm; path; reachability; transitive closure", } @Article{Gottlob:2008:BBA, author = "Georg Gottlob and Marko Samer", title = "A backtracking-based algorithm for hypertree decomposition", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "1:1--1:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412229", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Hypertree decompositions of hypergraphs are a generalization of tree decompositions of graphs. The corresponding hypertree-width is a measure for the acyclicity and therefore an indicator for the tractability of the associated computation problem. Several NP-hard decision and computation problems are known to be tractable on instances whose structure is represented by hypergraphs of bounded hypertree-width. Roughly speaking, the smaller the hypertree-width, the faster the computation problem can be solved. In this paper, we present the new backtracking-based algorithm det-$k$-decomp for computing hypertree decompositions of small width. Our benchmark evaluations have shown that det-$k$-decomp significantly outperforms opt- $k$-decomp, the only exact hypertree decomposition algorithm so far. Even compared to the best heuristic algorithm, we obtained competitive results as long as the hypergraphs are sufficiently simple.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "constraint satisfaction; hypertree decomposition", } @Article{Raman:2008:P, author = "Rajeev Raman and Matt Stallmann", title = "Preface", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "1:1--1:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412235", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Gramm:2008:DRE, author = "Jens Gramm and Jiong Guo and Falk H{\"u}ffner and Rolf Niedermeier", title = "Data reduction and exact algorithms for clique cover", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "2:1--2:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412236", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "To cover the edges of a graph with a minimum number of cliques is an NP-hard problem with many applications. For this problem we develop efficient and effective polynomial-time data reduction rules that, combined with a search tree algorithm, allow for exact problem solutions in competitive time. This is confirmed by experiments with real-world and synthetic data. Moreover, we prove the fixed-parameter tractability of covering edges by cliques.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "clique cover; data reduction; fixed-parameter tractability", } @Article{Haran:2008:ESP, author = "Idit Haran and Dan Halperin", title = "An experimental study of point location in planar arrangements in {CGAL}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "3:1--3:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412237", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study the performance in practice of various point-location algorithms implemented in CGAL (the Computational Geometry Algorithms Library), including a newly devised {\em landmarks\/} algorithm. Among the other algorithms studied are: a na{\"\i}ve approach, a ``walk along a line'' strategy, and a trapezoidal decomposition-based search structure. The current implementation addresses general arrangements of planar curves, including arrangements of nonlinear segments (e.g., conic arcs) and allows for degenerate input (for example, more than two curves intersecting in a single point or overlapping curves). The algorithms use exact geometric computation and thus result in the correct point location. In our landmarks algorithm (a.k.a. jump \& walk), special points, ``landmarks,'' are chosen in a preprocessing stage, their place in the arrangement is found, and they are inserted into a data structure that enables efficient nearest-neighbor search. Given a query point, the nearest landmark is located and a ``walk'' strategy is applied from the landmark to the query point. We report on various experiments with arrangements composed of line segments or conic arcs. The results indicate that compared to the other algorithms tested, the landmarks approach is the most efficient, when the overall (amortized) cost of a query is taken into account, combining both preprocessing and query time. The simplicity of the algorithm enables an almost straightforward implementation and rather easy maintenance. The generic programming implementation allows versatility both in the selected type of landmarks and in the choice of the nearest-neighbor search structure. The end result is an efficient point-location algorithm that bypasses the alternative CGAL implementations in most practical aspects.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "arrangements; CGAL; computational geometry; generic programming; point location", } @Article{Lanthier:2008:CAC, author = "Mark A. Lanthier and Doron Nussbaum and Tsuo-Jung Wang", title = "Computing an approximation of the $1$-center problem on weighted terrain surfaces", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "3:1--3:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412231", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this article, we discuss the problem of determining a meeting point of a set of scattered robots $R = r_1, r _2, \ldots{}, r_s$ in a weighted terrain $P$, which has $n > s$ triangular faces. Our algorithmic approach is to produce a discretization of $P$ by producing a graph $G = \{V^G, E^G\}$, which lies on the surface of $P$. For a chosen vertex $p' \in V^G$, we define $|\Pi(r_i, p')|$ as the minimum weight cost of traveling from $r_i$ to $p'$. We show that min$_{p'} \in V^G$ \hbox{max}$_{1\leq i \leq s} |\Pi(r_i, p')| \leq \hbox{min}_p *\in P \hbox{max}_{1\leq i \leq s} |{\Pi}(r_i, p*)| + 2 W |L|$, where $L$ is the longest edge of $P$, $W$ is the maximum cost weight of a face of $P$, and $p*$ is the optimal solution. Our algorithm requires $O(s n m \log(s n m) + s n m^2)$ time to run, where $m = n$ in the Euclidean metric and $m = n^2$ in the weighted metric. However, we show, through experimentation, that only a constant value of $m$ is required (e.g., $m = 8$) in order to produce very accurate solutions.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "1-Center; algorithms; approximation; meeting point; robots; shortest path; terrain; weighted", } @Article{Hershberger:2008:SSD, author = "John Hershberger and Nisheeth Shrivastava and Subhash Suri", title = "Summarizing spatial data streams using {ClusterHulls}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "4:1--4:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412238", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider the following problem: given an on-line, possibly unbounded stream of two-dimensional (2D) points, how can we summarize its spatial distribution or {\em shape\/} using a small, bounded amount of memory? We propose a novel scheme, called {\em ClusterHull}, which represents the shape of the stream as a dynamic collection of convex hulls, with a total of at most $m$ vertices, where $m$ is the size of the memory. The algorithm dynamically adjusts both the number of hulls and the number of vertices in each hull to best represent the stream using its fixed-memory budget. This algorithm addresses a problem whose importance is increasingly recognized, namely, the problem of summarizing real-time data streams to enable on-line analytical processing. As a motivating example, consider habitat monitoring using wireless sensor networks. The sensors produce a steady stream of geographic data, namely, the locations of objects being tracked. In order to conserve their limited resources (power, bandwidth, and storage), the sensors can compute, store, and exchange ClusterHull summaries of their data, without losing important geometric information. We are not aware of other schemes specifically designed for capturing shape information in geometric data streams and so we compare ClusterHull with some of the best general-purpose clustering schemes, such as CURE, $k$-medians, and LSEARCH. We show through experiments that ClusterHull is able to represent the shape of two-dimensional data streams more faithfully and flexibly than the stream versions of these clustering algorithms.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "convex hull; data streams; geometric data", } @Article{Safro:2008:MAL, author = "Ilya Safro and Dorit Ron and Achi Brandt", title = "Multilevel algorithms for linear ordering problems", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "4:1--4:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412232", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Linear ordering problems are combinatorial optimization problems that deal with the minimization of different functionals by finding a suitable permutation of the graph vertices. These problems are widely used and studied in many practical and theoretical applications. In this paper, we present a variety of linear--time algorithms for these problems inspired by the Algebraic Multigrid approach, which is based on weighted-edge contraction. The experimental result for four such problems turned out to be better than every known result in almost all cases, while the short (linear) running time of the algorithms enables testing very large graphs.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algebraic multigrid; linear ordering; multilevel algorithm", } @Article{Holzer:2008:EMO, author = "Martin Holzer and Frank Schulz and Dorothea Wagner", title = "Engineering multilevel overlay graphs for shortest-path queries", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "13", pages = "5:1--5:??", month = sep, year = "2008", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1412228.1412239", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Oct 6 16:18:31 MDT 2008", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "An overlay graph of a given graph $G$ = ($V$, $E$) on a subset $S \subseteq V$ is a graph with vertex set $S$ and edges corresponding to shortest paths in $G$. In particular, we consider variations of the multilevel overlay graph used in Schulz et al. [2002] to speed up shortest-path computation. In this work, we follow up and present several vertex selection criteria, along with two general strategies of applying these criteria, to determine a subset $S$ of a graph's vertices. The main contribution is a systematic experimental study where we investigate the impact of selection criteria and strategies on multilevel overlay graphs and the resulting speed-up achieved for shortest-path computation: Depending on selection strategy and graph type, a centrality index criterion, selection based on planar separators, and vertex degree turned out to perform best.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "Dijkstra's algorithm; hierarchical; multilevel; overlay graph; preprocessing; shortest path; speed-up technique; vertex selection", } @Article{Julstrom:2009:GHB, author = "Bryant A. Julstrom", title = "Greedy heuristics for the bounded diameter minimum spanning tree problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "1:1--1:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Given a connected, weighted, undirected graph G and a bound $D$, the bounded diameter minimum spanning tree problem seeks a spanning tree on $G$ of minimum weight among the trees in which no path between two vertices contains more than $D$ edges. In Prim's algorithm, the diameter of the growing spanning tree can always be known, so it is a good starting point from which to develop greedy heuristics for the bounded diameter problem. Abdalla, Deo, and Gupta described such an algorithm. It imitates Prim's algorithm but avoids edges whose inclusion in the spanning tree would violate the diameter bound. Running the algorithm from one start vertex requires time that is $O(n^3)$. A modification of this approach uses the start vertex as the center of the spanning tree (if $D$ is even) or as one of the two center vertices (if $D$ is odd). This yields a simpler algorithm whose time is $O(n^2)$. A further modification chooses each next vertex at random rather than greedily, though it still connects each vertex to the growing tree with the lowest-weight feasible edge. On Euclidean problem instances with small diameter bounds, the randomized heuristic is superior to the two fully greedy algorithms, though its advantage fades as the diameter bound grows. On instances whose edge weights have been chosen at random, the fully greedy algorithms outperform the randomized heuristic.", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Munro:2009:PSS, author = "J. Ian Munro and Dorothea Wagner", title = "Preface: Section 2 --- Selected Papers from {ALENEX 2008}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "1:1--1:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Dumitriu:2009:HMG, author = "Daniel Dumitriu and Stefan Funke and Martin Kutz and Nikola Milosavljevi{\'c}", title = "How much geometry it takes to reconstruct a $2$-manifold in {$R^3$}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "2:1--2:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Known algorithms for reconstructing a 2-manifold from a point sample in $R^3$ are naturally based on decisions/predicates that take the geometry of the point sample into account. Facing the always present problem of round-off errors that easily compromise the exactness of those predicate decisions, an exact and robust implementation of these algorithms is far from being trivial and typically requires employment of advanced datatypes for exact arithmetic, as provided by libraries like CORE, LEDA, or GMP. In this article, we present a new reconstruction algorithm, one whose main novelties is to throw away geometry information early on in the reconstruction process and to mainly operate combinatorially on a graph structure. More precisely, our algorithm only requires distances between the sample points and not the actual embedding in $R^3$. As such, it is less susceptible to robustness problems due to round-off errors and also benefits from not requiring expensive exact arithmetic by faster running times. A more theoretical view on our algorithm including correctness proofs under suitable sampling conditions can be found in a companion article.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Irving:2009:FLS, author = "Robert W. Irving and David F. Manlove", title = "Finding large stable matchings", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "2:1--2:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "When ties and incomplete preference lists are permitted in the stable marriage and hospitals/residents problems, stable matchings can have different sizes. The problem of finding a maximum cardinality stable matching in this context is known to be NP-hard, even under very severe restrictions on the number, size, and position of ties. In this article, we present two new heuristics for finding large stable matchings in variants of these problems in which ties are on one side only. We describe an empirical study involving these heuristics and the best existing approximation algorithm for this problem. Our results indicate that all three of these algorithms perform significantly better than naive tie-breaking algorithms when applied to real-world and randomly-generated data sets and that one of the new heuristics fares slightly better than the other algorithms, in most cases. This study, and these particular problem variants, are motivated by important applications in large-scale centralized matching schemes.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Basu:2009:GAO, author = "Amitabh Basu and Joseph S. B. Mitchell and Girish Kumar Sabhnani", title = "Geometric algorithms for optimal airspace design and air traffic controller workload balancing", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "3:1--3:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The National Airspace System (NAS) is designed to accommodate a large number of flights over North America. For purposes of workload limitations for air traffic controllers, the airspace is partitioned into approximately 600 sectors; each sector is observed by one or more controllers. In order to satisfy workload limitations for controllers, it is important that sectors be designed carefully according to the traffic patterns of flights, so that no sector becomes overloaded. We formulate and study the airspace sectorization problem from an algorithmic point-of-view, modeling the problem of optimal sectorization as a geometric partition problem with constraints. The novelty of the problem is that it partitions data consisting of trajectories of moving points, rather than static point set partitioning that is commonly studied. First, we formulate and solve the 1D version of the problem, showing how to partition a line into ``sectors'' (intervals) according to historical trajectory data. Then, we apply the 1D solution framework to design a 2D sectorization heuristic based on binary space partitions. We also devise partitions based on balanced ``pie partitions'' of a convex polygon. We evaluate our 2D algorithms experimentally, applying our algorithms to actual historical flight track data for the NAS. We compare the workload balance of our methods to that of the existing set of sectors for the NAS and find that our resectorization yields competitive and improved workload balancing. In particular, our methods yield an improvement by a factor between 2 and 3 over the current sectorization in terms of the time-average and the worst-case workloads of the maximum workload sector. An even better improvement is seen in the standard deviations (over all sectors) of both time-average and worst-case workloads.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Bauer:2009:SFR, author = "Reinhard Bauer and Daniel Delling", title = "{SHARC}: Fast and robust unidirectional routing", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "4:1--4:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "During recent years, impressive speed-up techniques for Dijkstra's have been developed. Unfortunately, the most advanced techniques use bidirectional search, which makes it hard to use them in scenarios where a backward search is prohibited. Even worse, such scenarios are widely spread (e.g., timetable-information systems or time-dependent networks). In this work, we present a unidirectional speed-up technique, which competes with bidirectional approaches. Moreover, we show how to exploit the advantage of unidirectional routing for fast exact queries in timetable information systems and for fast approximative queries in time-dependent scenarios. By running experiments on several inputs other than road networks, we show that our approach is very robust to the input.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Coleman:2009:RTL, author = "Tom Coleman and Anthony Wirth", title = "Ranking tournaments: Local search and a new algorithm", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "6:1--6:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Ranking is a fundamental activity for organizing and, later, understanding data. Advice of the form ``$a$ should be ranked before $b$'' is given. If this advice is consistent, and complete, then there is a total ordering on the data and the ranking problem is essentially a sorting problem. If the advice is consistent, but incomplete, then the problem becomes topological sorting. If the advice is inconsistent, then we have the feedback arc set (FAS) problem: The aim is then to rank a set of items to satisfy as much of the advice as possible. An instance in which there is advice about every pair of items is known as a tournament. This ranking task is equivalent to ordering the nodes of a given directed graph from left to right, while minimizing the number of arcs pointing left. In the past, much work focused on finding good, effective heuristics for solving the problem. Recently, a proof of the NP-completeness of the problem (even when restricted to tournaments) has accompanied new algorithms with approximation guarantees, culminating in the development of a PTAS (polynomial time approximation scheme) for solving FAS on tournaments. In this article, we reexamine many existing algorithms and develop some new techniques for solving FAS. The algorithms are tested on both synthetic and nonsynthetic datasets. We find that, in practice, local-search algorithms are very powerful, even though we prove that they do not have approximation guarantees. Our new algorithm is based on reversing arcs whose nodes have large in-degree differences, eventually leading to a total ordering. Combining this with a powerful local-search technique yields an algorithm that is as strong, or stronger than, existing techniques on a variety of data sets.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Cherkassky:2009:SPF, author = "Boris V. Cherkassky and Loukas Georgiadis and Andrew V. Goldberg and Robert E. Tarjan and Renato F. Werneck", title = "Shortest-path feasibility algorithms: An experimental evaluation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", pages = "7:1--7:??", month = may, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jun 3 16:21:43 MDT 2009", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "This is an experimental study of algorithms for the shortest-path feasibility problem: Given a directed weighted graph, find a negative cycle or present a short proof that none exists. We study previously known and new algorithms. Our testbed is more extensive than those previously used, including both static and incremental problems, as well as worst-case instances. We show that, while no single algorithm dominates, a small subset (including new algorithms) has very robust performance in practice. Our work advances the state of the art in the area.", acknowledgement = ack-nhfb, articleno = "7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Demetrescu:2009:P, author = "Camil Demetrescu", title = "Preface", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "1:1--1:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Serna:2009:PSS, author = "Maria Serna and Carme {\'A}lvarez", title = "Preface to special section of selected papers from {WEA 2006}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "1:1--1:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Maue:2009:GDS, author = "Jens Maue and Peter Sanders and Domagoj Matijevic", title = "Goal-directed shortest-path queries using precomputed cluster distances", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "2:1--2:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We demonstrate how Dijkstra's algorithm for shortest path queries can be accelerated by using precomputed shortest path distances. Our approach allows a completely flexible tradeoff between query time and space consumption for precomputed distances. In particular, sublinear space is sufficient to give the search a strong ``sense of direction''. We evaluate our approach experimentally using large, real-world road networks.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Valimaki:2009:ECS, author = "N. V{\"a}lim{\"a}ki and V. M{\"a}kinen and W. Gerlach and K. Dixit", title = "Engineering a compressed suffix tree implementation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "2:1--2:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Suffix tree is one of the most important data structures in string algorithms and biological sequence analysis. Unfortunately, when it comes to implementing those algorithms and applying them to real genomic sequences, often the main memory size becomes the bottleneck. This is easily explained by the fact that while a DNA sequence of length $n$ from alphabet $\Sigma = \{ A, C, G, T \}$ can be stored in $n \log |\Sigma| = 2 n$ bits, its suffix tree occupies $O(n \log n)$ bits. In practice, the size difference easily reaches factor 50. We report on an implementation of the compressed suffix tree very recently proposed by Sadakane (2007). The compressed suffix tree occupies space proportional to the text size, that is, $O(n \log |\Sigma|)$ bits, and supports all typical suffix tree operations with at most $\log n$ factor slowdown. Our experiments show that, for example, on a 10 MB DNA sequence, the compressed suffix tree takes 10\% of the space of the normal suffix tree. At the same time, a representative algorithm is slowed down by factor 30. Our implementation follows the original proposal in spirit, but some internal parts are tailored toward practical implementation. Our construction algorithm has time requirement $O(n \log n \log |\Sigma|)$ and uses closely the same space as the final structure while constructing it: on the 10MB DNA sequence, the maximum space usage during construction is only 1.5 times the final product size. As by-products, we develop a method to create Succinct Suffix Array directly from Burrows--Wheeler transform and a space-efficient version of the suffixes-insertion algorithm to build balanced parentheses representation of suffix tree from LCP information.", acknowledgement = ack-nhfb, articleno = "2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Eisenbrand:2009:ALO, author = "Friedrich Eisenbrand and Andreas Karrenbauer and Chihao Xu", title = "Algorithms for longer {OLED} lifetime", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "3:1--3:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider an optimization problem arising in the design of controllers for OLED displays. Our objective is to minimize the amplitude of the electrical current flowing through the diodes, which has a direct impact on the lifetime of such a display. The optimization problem consist of finding a decomposition of an image into subframes with special structural properties that allow the display driver to lower the stress on the diodes. For monochrome images, we present an algorithm that finds an optimal solution of this problem in linear time. Moreover, we consider an online version of the problem in which we have to take a decision for one row based on a constant number of rows in the lookahead. In this framework, this algorithm has a tight competitive ratio. A generalization of this algorithm computes near-optimal solutions of real-world instances in real time.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Englert:2009:EOS, author = "Matthias Englert and Heiko R{\"o}glin and Matthias Westermann", title = "Evaluation of online strategies for reordering buffers", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "3:1--3:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A sequence of objects that are characterized by their color has to be processed. Their processing order influences how efficiently they can be processed: Each color change between two consecutive objects produces costs. A reordering buffer, which is a random access buffer with storage capacity for k objects, can be used to rearrange this sequence online in such a way that the total costs are reduced. This concept is useful for many applications in computer science and economics. The strategy with the best-known competitive ratio is MAP. An upper bound of $O(\log k)$ on the competitive ratio of MAP is known and a nonconstant lower bound on the competitive ratio is not known. Based on theoretical considerations and experimental evaluations, we give strong evidence that the previously used proof techniques are not suitable to show an $o (\sqrt{\log k})$ upper bound on the competitive ratio of MAP. However, we also give some evidence that in fact MAP achieves a competitive ratio of $O(1)$. Further, we evaluate the performance of several strategies on random input sequences experimentally. MAP and its variants RC and RR clearly outperform the other strategies FIFO, LRU, and MCF. In particular, MAP, RC, and RR are the only known strategies whose competitive ratios do not depend on the buffer size. Furthermore, MAP achieves the smallest competitive ratio.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Farshi:2009:ESG, author = "Mohammad Farshi and Joachim Gudmundsson", title = "Experimental study of geometric $t$-spanners", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "3:1--3:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The construction of t -spanners of a given point set has received a lot of attention, especially from a theoretical perspective. In this article, we experimentally study the performance and quality of the most common construction algorithms for points in the Euclidean plane. We implemented the most well-known t -spanner algorithms and tested them on a number of different point sets. The experiments are discussed and compared to the theoretical results, and in several cases, we suggest modifications that are implemented and evaluated. The measures of quality that we consider are the number of edges, the weight, the maximum degree, the spanner diameter, and the number of crossings. This is the first time an extensive comparison has been made between the running times of construction algorithms of t -spanners and the quality of the generated spanners.", acknowledgement = ack-nhfb, articleno = "3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Cederman:2009:GQP, author = "Daniel Cederman and Philippas Tsigas", title = "{GPU-Quicksort}: a practical {Quicksort} algorithm for graphics processors", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "4:1--4:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this article, we describe GPU-Quicksort, an efficient Quicksort algorithm suitable for highly parallel multicore graphics processors. Quicksort has previously been considered an inefficient sorting solution for graphics processors, but we show that in CUDA, NVIDIA's programming platform for general-purpose computations on graphical processors, GPU-Quicksort performs better than the fastest-known sorting implementations for graphics processors, such as radix and bitonic sort. Quicksort can thus be seen as a viable alternative for sorting large quantities of data on graphics processors.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Chimani:2009:EEC, author = "Markus Chimani and Carsten Gutwenger and Petra Mutzel", title = "Experiments on exact crossing minimization using column generation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "4:1--4:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The crossing number of a graph G is the smallest number of edge crossings in any drawing of G into the plane. Recently, the first branch-and-cut approach for solving the crossing number problem has been presented in Buchheim et al. [2005]. Its major drawback was the huge number of variables out of which only very few were actually used in the optimal solution. This restricted the algorithm to rather small graphs with low crossing number. In this article, we discuss two column generation schemes; the first is based on traditional algebraic pricing, and the second uses combinatorial arguments to decide whether and which variables need to be added. The main focus of this article is the experimental comparison between the original approach and these two schemes. In addition, we evaluate the quality achieved by the best-known crossing number heuristic by comparing the new results with the results of the heuristic.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Putze:2009:CHS, author = "Felix Putze and Peter Sanders and Johannes Singler", title = "Cache-, hash-, and space-efficient {Bloom} filters", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "4:1--4:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A Bloom filter is a very compact data structure that supports approximate membership queries on a set, allowing false positives. We propose several new variants of Bloom filters and replacements with similar functionality. All of them have a better cache-efficiency and need less hash bits than regular Bloom filters. Some use SIMD functionality, while the others provide an even better space efficiency. As a consequence, we get a more flexible trade-off between false-positive rate, space-efficiency, cache-efficiency, hash-efficiency, and computational effort. We analyze the efficiency of Bloom filters and the proposed replacements in detail, in terms of the false-positive rate, the number of expected cache-misses, and the number of required hash bits. We also describe and experimentally evaluate the performance of highly tuned implementations. For many settings, our alternatives perform better than the methods proposed so far.", acknowledgement = ack-nhfb, articleno = "4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Chimani:2009:OOC, author = "Markus Chimani and Maria Kandyba and Ivana Ljubi{\'c} and Petra Mutzel", title = "Obtaining optimal $k$-cardinality trees fast", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "2.5:1--2.5:23", month = dec, year = "2009", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1498698.1537600", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Given an undirected graph G = (V, E) with edge weights and a positive integer number k, the k -cardinality tree problem consists of finding a subtree T of G with exactly k edges and the minimum possible weight. Many algorithms have been proposed to solve this NP-hard problem, resulting in mainly heuristic and metaheuristic approaches. In this article, we present an exact ILP-based algorithm using directed cuts. We mathematically compare the strength of our formulation to the previously known ILP formulations of this problem, and show the advantages of our approach. Afterwards, we give an extensive study on the algorithm's practical performance compared to the state-of-the-art metaheuristics. In contrast to the widespread assumption that such a problem cannot be efficiently tackled by exact algorithms for medium and large graphs (between 200 and 5,000 nodes), our results show that our algorithm not only has the advantage of proving the optimality of the computed solution, but also often outperforms the metaheuristic approaches in terms of running time.", acknowledgement = ack-nhfb, articleno = "2.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Frias:2009:LRC, author = "Leonor Frias and Jordi Petit and Salvador Roura", title = "Lists revisited: Cache-conscious {STL} lists", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "5:1--5:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present three cache-conscious implementations of STL standard compliant lists. Until now, one could either find simple doubly linked list implementations that easily cope with standard strict requirements, or theoretical approaches that do not take into account any of these requirements in their design. In contrast, we have merged both approaches, paying special attention to iterators constraints. In this article, the competitiveness of our implementations is evinced with an extensive experimental analysis. This shows, for instance, 5 to 10 times faster traversals and 3 to 5 times faster internal sort.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Holzer:2009:EPS, author = "Martin Holzer and Frank Schulz and Dorothea Wagner and Grigorios Prasinos and Christos Zaroliagis", title = "Engineering planar separator algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "5:1--5:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider classical linear-time planar separator algorithms, determining for a given planar graph a small subset of its nodes whose removal divides the graph into two components of similar size. These algorithms are based on planar separator theorems, which guarantee separators of size $O(\sqrt n)$ and remaining components of size at most $2 n / 3$ (where $n$ denotes the number of nodes in the graph). In this article, we present a comprehensive experimental study of the classical algorithms applied to a large variety of graphs, where our main goal is to find separators that do not only satisfy upper bounds, but also possess other desirable characteristics with respect to separator size and component balance. We achieve this by investigating a number of specific alternatives for the concrete implementation and fine-tuning of certain parts of the classical algorithms. It is also shown that the choice of several parameters influences the separation quality considerably. Moreover, we propose as planar separators the usage of fundamental cycles, whose size is at most twice the diameter of the graph: For graphs of small diameter, the guaranteed bound is better than the $O(\sqrt n)$ bounds, and it turns out that this simple strategy almost always outperforms the other algorithms, even for graphs with large diameter.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Tarjan:2009:DTP, author = "Robert E. Tarjan and Renato F. Werneck", title = "Dynamic trees in practice", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "5:1--5:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Dynamic tree data structures maintain forests that change over time through edge insertions and deletions. Besides maintaining connectivity information in logarithmic time, they can support aggregation of information over paths, trees, or both. We perform an experimental comparison of several versions of dynamic trees: ST-trees, ET-trees, RC-trees, and two variants of top trees (self-adjusting and worst-case). We quantify their strengths and weaknesses through tests with various workloads, most stemming from practical applications. We observe that a simple, linear-time implementation is remarkably fast for graphs of small diameter, and that worst-case and randomized data structures are best when queries are very frequent. The best overall performance, however, is achieved by self-adjusting ST-trees.", acknowledgement = ack-nhfb, articleno = "5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Avdil:2009:LSS, author = "Alaubek Avdil and Karsten Weihe", title = "Local search starting from an {LP} solution: Fast and quite good", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "6:1--6:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present and evaluate a specific way to generate good start solutions for local search. The start solution is computed from a certain LP, which is related to the underlying problem. We consider three optimization problems: the directed MAX-CUT problem with a source and a sink and two variations of the MAX- k -SAT problem with k = 2 and k = 3. To compare our technique, we run local search repeatedly with random start solutions. Our technique produces, consistently, final solutions whose objective values are not too far from the best solutions from repeated random starts. The surprising degree of stability and uniformity of this result throughout all of our experiments on various classes of instances strongly suggests that we have consistently achieved nearly optimal solutions. On the other hand, the runtime of our technique is rather small, so the technique is very efficient and probably quite accurate.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Deineko:2009:FMW, author = "Vladimir Deineko and Alexander Tiskin", title = "Fast minimum-weight double-tree shortcutting for metric {TSP}: Is the best one good enough?", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "6:1--6:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The Metric Traveling Salesman Problem (TSP) is a classical NP-hard optimization problem. The double-tree shortcutting method for Metric TSP yields an exponentially-sized space of TSP tours, each of which approximates the optimal solution within, at most, a factor of 2. We consider the problem of finding among these tours the one that gives the closest approximation, that is, the minimum-weight double-tree shortcutting. Burkard et al. gave an algorithm for this problem, running in time $O(n^3 + 2^d n^2)$ and memory $O(2^d n^2)$, where $d$ is the maximum node degree in the rooted minimum spanning tree. We give an improved algorithm for the case of small $d$ (including planar Euclidean TSP, where $d \leq 4$), running in time $O(4^d n^2)$ and memory $O(4^d n)$. This improvement allows one to solve the problem on much larger instances than previously attempted. Our computational experiments suggest that in terms of the time-quality trade-off, the minimum-weight double-tree shortcutting method provides one of the best existing tour-constructing heuristics.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Figueroa:2009:SSA, author = "Karina Figueroa and Edgar Chavez and Gonzalo Navarro and Rodrigo Paredes", title = "Speeding up spatial approximation search in metric spaces", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "6:1--6:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Proximity searching consists of retrieving from a database those elements that are similar to a query object. The usual model for proximity searching is a metric space where the distance, which models the proximity, is expensive to compute. An index uses precomputed distances to speedup query processing. Among all the known indices, the baseline for performance for about 20 years has been AESA. This index uses an iterative procedure, where at each iteration it first chooses the next promising element (``pivot'') to compare to the query, and then it discards database elements that can be proved not relevant to the query using the pivot. The next pivot in AESA is chosen as the one minimizing the sum of lower bounds to the distance to the query proved by previous pivots. In this article, we introduce the new index iAESA, which establishes a new performance baseline for metric space searching. The difference with AESA is the method to select the next pivot. In iAESA, each candidate sorts previous pivots by closeness to it, and chooses the next pivot as the candidate whose order is most similar to that of the query. We also propose a modification to AESA-like algorithms to turn them into probabilistic algorithms. Our empirical results confirm a consistent improvement in query performance. For example, we perform as few as 60\% of the distance evaluations of AESA in a database of documents, a very important and difficult real-life instance of the problem. For the probabilistic algorithm, we perform in a database of faces up to 40\% of the comparisons made by the best alternative algorithm to retrieve the same percentage of the correct answer. Based on the empirical results, we conjecture that the new probabilistic AESA-like algorithms will become, as AESA had been for exact algorithms, a reference point establishing, in practice, a lower bound on how good a probabilistic proximity search algorithm can be.", acknowledgement = ack-nhfb, articleno = "6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Barbay:2009:EIS, author = "J{\'e}r{\'e}my Barbay and Alejandro L{\'o}pez-Ortiz and Tyler Lu and Alejandro Salinger", title = "An experimental investigation of set intersection algorithms for text searching", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "7:1--7:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The intersection of large ordered sets is a common problem in the context of the evaluation of boolean queries to a search engine. In this article, we propose several improved algorithms for computing the intersection of sorted arrays, and in particular for searching sorted arrays in the intersection context. We perform an experimental comparison with the algorithms from the previous studies from Demaine, L{\'o}pez-Ortiz, and Munro [ALENEX 2001] and from Baeza-Yates and Salinger [SPIRE 2005]; in addition, we implement and test the intersection algorithm from Barbay and Kenyon [SODA 2002] and its randomized variant [SAGA 2003]. We consider both the random data set from Baeza-Yates and Salinger, the Google queries used by Demaine et al., a corpus provided by Google, and a larger corpus from the TREC Terabyte 2006 efficiency query stream, along with its own query log. We measure the performance both in terms of the number of comparisons and searches performed, and in terms of the CPU time on two different architectures. Our results confirm or improve the results from both previous studies in their respective context (comparison model on real data, and CPU measures on random data) and extend them to new contexts. In particular, we show that value-based search algorithms perform well in posting lists in terms of the number of comparisons performed.", acknowledgement = ack-nhfb, articleno = "7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Estivill-Castro:2009:RRD, author = "Vladimir Estivill-Castro and Apichat Heednacram and Francis Suraweera", title = "Reduction rules deliver efficient {FPT}-algorithms for covering points with lines", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "7:1--7:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present efficient algorithms to solve the Line Cover Problem exactly. In this NP-complete problem, the inputs are n points in the plane and a positive integer k, and we are asked to answer if we can cover these n points with at most k lines. Our approach is based on fixed-parameter tractability and, in particular, kernelization. We propose several reduction rules to transform instances of Line Cover into equivalent smaller instances. Once instances are no longer susceptible to these reduction rules, we obtain a problem kernel whose size is bounded by a polynomial function of the parameter k and does not depend on the size n of the input. Our algorithms provide exact solutions and are easy to implement. We also describe the design of algorithms to solve the corresponding optimization problem exactly. We experimentally evaluated ten variants of the algorithms to determine the impact and trade-offs of several reduction rules. We show that our approach provides tractability for a larger range of values of the parameter and larger inputs, improving the execution time by several orders of magnitude with respect to earlier algorithms that use less rules.", acknowledgement = ack-nhfb, articleno = "7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{DeLoera:2009:CMM, author = "Jes{\'u}s A. {De Loera} and David C. Haws and Jon Lee and Allison O'Hair", title = "Computation in multicriteria matroid optimization", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "14", number = "1", pages = "8:1--8:??", month = dec, year = "2009", CODEN = "????", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:04:28 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Motivated by recent work on algorithmic theory for nonlinear and multicriteria matroid optimization, we have developed algorithms and heuristics aimed at practical solution of large instances of some of these difficult problems. Our methods primarily use the local adjacency structure inherent in matroid polytopes to pivot to feasible solutions, which may or may not be optimal. We also present a modified breadth-first-search heuristic that uses adjacency to enumerate a subset of feasible solutions. We present other heuristics and provide computational evidence supporting our techniques. We implemented all of our algorithms in the software package MOCHA.", acknowledgement = ack-nhfb, articleno = "8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Jacobs:2010:ESR, author = "Tobias Jacobs", title = "An experimental study of recent hotlink assignment algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "1.1:1--1.1:??", month = mar, year = "2010", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1671970.1671971", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:05:50 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The concept of {\em hotlink assignment\/} aims at enhancing the structure of Web sites such that the user's expected navigation effort is minimized. We concentrate on sites that are representable by trees and assume that each leaf carries a weight representing its popularity.\par The problem of optimally adding at most one additional outgoing edge (``hotlink'') to each inner node has been widely studied. A considerable number of approximation algorithms have been proposed and worst-case bounds for the quality of the computed solutions have been given. However, only little is known about the practical behavior of most of these algorithms.\par This article contributes to closing this gap by evaluating all recently proposed strategies experimentally. Our experiments are based on trees extracted from real Web sites, as well as on synthetic instances. The latter are generated by a new method that simulates the growth of a Web site over time. Finally, we present a new heuristic that is easy to implement and exhibits excellent behavior in practice.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "approximation; hotlink; Search tree", } @Article{Spence:2010:SGS, author = "Ivor Spence", title = "{{\tt sgen1}}: a generator of small but difficult satisfiability benchmarks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "1.2:1--1.2:??", month = mar, year = "2010", CODEN = "????", DOI = "http://doi.acm.org/10.1145/1671970.1671972", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:05:50 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The satisfiability problem is known to be NP-Complete; therefore, there should be relatively small problem instances that take a very long time to solve. However, most of the smaller benchmarks that were once thought challenging, especially the satisfiable ones, can be processed quickly by modern SAT-solvers. We describe and make available a generator that produces both unsatisfiable and, more significantly, satisfiable formulae that take longer to solve than any others known. At the two most recent international SAT Competitions, the smallest unsolved benchmarks were created by this generator. We analyze the results of all solvers in the most recent competition when applied to these benchmarks and also present our own more focused experiments.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "SAT-solvers; Satisfiability benchmarks", } @Article{Langguth:2010:HIB, author = "Johannes Langguth and Fredrik Manne and Peter Sanders", title = "Heuristic initialization for bipartite matching problems", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "1.3:1--1.3:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1712655.1712656", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Mar 15 12:05:50 MDT 2010", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "It is a well-established result that improved pivoting in linear solvers can be achieved by computing a bipartite matching between matrix entries and positions on the main diagonal. With the availability of increasingly faster linear solvers, the speed of bipartite matching computations must keep up to avoid slowing down the main computation. Fast algorithms for bipartite matching, which are usually initialized with simple heuristics, have been known for a long time. However, the performance of these algorithms is largely dependent on the quality of the heuristic. We compare combinations of several known heuristics and exact algorithms to find fast combined methods, using real-world matrices as well as randomly generated instances. In addition, we present a new heuristic aimed at obtaining high-quality matchings and compare its impact on bipartite matching algorithms with that of other heuristics. The experiments suggest that its performance compares favorably to the best-known heuristics, and that it is especially suited for application in linear solvers.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "Heuristics; matching", } @Article{Delbot:2010:AEC, author = "Fran{\c{c}}ois Delbot and Christian Laforest", title = "Analytical and experimental comparison of six algorithms for the vertex cover problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "14:1--14:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1865970.1865971", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The vertex cover is a well-known NP-complete minimization problem in graphs that has received a lot of attention these last decades. Many algorithms have been proposed to construct vertex cover in different contexts (offline, online, list algorithms, etc.) leading to solutions of different level of quality. This quality is traditionally measured in terms of approximation ratio, that is, the worst possible ratio between the quality of the solution constructed and the optimal one. For the vertex cover problem the range of such known ratios are between 2 (conjectured as being the smallest constant ratio) and $\Delta$, the maximum degree of the graph. Based on this measure of quality, the hierarchy is almost clear (the smaller the ratio is, the better the algorithm is). In this article, we show that this measure, although of great importance, is too macroscopic and does not reflect the practical behavior of the methods. We prove this by analyzing (known and recent) algorithms running on a particular class of graphs: the paths. We obtain closed and exact formulas for the mean of the sizes of vertex cover constructed by these different algorithms. Then, we assess their quality experimentally in several well-chosen class of graphs (random, regular, trees, BHOSLIB benchmarks, trap graphs, etc.). The synthesis of all these results lead us to formulate a ``practical hierarchy'' of the algorithms. We remark that it is, more or less, the opposite to the one only based on approximation ratios, showing that worst-case analysis only gives partial information on the quality of an algorithm.", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Arroyuelo:2010:PAR, author = "Diego Arroyuelo and Gonzalo Navarro", title = "Practical approaches to reduce the space requirement of {Lempel--Ziv}-based compressed text indices", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "15:1--15:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1883684", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Given a text $T [1.\,.n]$ over an alphabet of size $\sigma$, the full-text search problem consists in locating the occ occurrences of a given pattern $P[1.\,.m]$ in $T$. Compressed full-text self-indices are space-efficient representations of the text that provide direct access to and indexed search on it.\par The LZ-index of Navarro is a compressed full-text self-index based on the LZ78 compression algorithm. This index requires about 5 times the size of the compressed text (in theory, $4 n H_k(T) + o(n \log \sigma)$ bits of space, where $H_k(T)$ is the $k$-th order empirical entropy of $T$). In practice, the average locating complexity of the LZ-index is $O(\sigma m \log_\sigma n + {\rm occ} \sigma^{m / 2})$, where {\em occ} is the number of occurrences of $P$. It can extract text substrings of length $l$ in $O(l)$ time. This index outperforms competing schemes both to locate short patterns and to extract text snippets. However, the LZ-index can be up to 4 times larger than the smallest existing indices (which use $n H_k(T) + o(n \log \sigma)$ bits in theory), and it does not offer space/time tuning options. This limits its applicability.\par In this article, we study practical ways to reduce the space of the LZ-index. We obtain new LZ-index variants that require $2(1 + \epsilon) n H_k(T) + o(n \log \sigma)$ bits of space, for any $0 < \epsilon < 1$. They have an average locating time of $O(1 / \epsilon (m \log n + {\rm occ} \sigma^{m / 2}))$, while extracting takes $O(l)$ time.\par We perform extensive experimentation and conclude that our schemes are able to reduce the space of the original LZ-index by a factor of $2/3$, that is, around $3$ times the compressed text size. Our schemes are able to extract about 1 to 2 MB of the text per second, being twice as fast as the most competitive alternatives. Pattern occurrences are located at a rate of up to 1 to 4 million per second. This constitutes the best space\slash time trade-off when indices are allowed to use 4 times the size of the compressed text or more.", acknowledgement = ack-nhfb, articleno = "1.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Ullmann:2010:BVA, author = "Julian R. Ullmann", title = "Bit-vector algorithms for binary constraint satisfaction and subgraph isomorphism", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "16:1--16:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1921702", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A solution to a binary constraint satisfaction problem is a set of discrete values, one in each of a given set of domains, subject to constraints that allow only prescribed pairs of values in specified pairs of domains. Solutions are sought by backtrack search interleaved with a process that removes from domains those values that are currently inconsistent with provisional choices already made in the course of search. For each value in a given domain, a bit-vector shows which values in another domain are or are not permitted in a solution. Bit-vector representation of constraints allows bit-parallel, therefore fast, operations for editing domains during search. This article revises and updates bit-vector algorithms published in the 1970's, and introduces focus search, which is a new bit-vector algorithm relying more on search and less on domain-editing than previous algorithms. Focus search is competitive within a limited family of constraint satisfaction problems. Determination of subgraph isomorphism is a specialized binary constraint satisfaction problem for which bit-vector algorithms have been widely used since the 1980s, particularly for matching molecular structures. This article very substantially updates the author's 1976 subgraph isomorphism algorithm, and reports experimental results with random and real-life data.", acknowledgement = ack-nhfb, articleno = "1.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Askitis:2010:RSH, author = "Nikolas Askitis and Justin Zobel", title = "Redesigning the string hash table, burst trie, and {BST} to exploit cache", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "17:1--17:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1921704", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "A key decision when developing in-memory computing applications is choice of a mechanism to store and retrieve strings. The most efficient current data structures for this task are the hash table with move-to-front chains and the burst trie, both of which use linked lists as a substructure, and variants of binary search tree. These data structures are computationally efficient, but typical implementations use large numbers of nodes and pointers to manage strings, which is not efficient in use of cache. In this article, we explore two alternatives to the standard representation: the simple expedient of including the string in its node, and, for linked lists, the more drastic step of replacing each list of nodes by a contiguous array of characters. Our experiments show that, for large sets of strings, the improvement is dramatic. For hashing, in the best case the total space overhead is reduced to less than 1 bit per string. For the burst trie, over 300MB of strings can be stored in a total of under 200MB of memory with significantly improved search time. These results, on a variety of data sets, show that cache-friendly variants of fundamental data structures can yield remarkable gains in performance.", acknowledgement = ack-nhfb, articleno = "1.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{McGeoch:2010:P, author = "Catherine C. McGeoch", title = "Preface", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "2.1:1--2.1:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1671974", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Chimani:2010:LFU, author = "Markus Chimani and Carsten Gutwenger and Petra Mutzel and Hoi-Ming Wong", title = "Layer-free upward crossing minimization", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "2.2:1--2.2:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1671975", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "An upward drawing of a DAG $G$ is a drawing of $G$ in which all arcs are drawn as curves increasing monotonically in the vertical direction. In this article, we present a new approach for upward crossing minimization, that is, finding an upward drawing of a DAG $G$ with as few crossings as possible. Our algorithm is based on a two-stage upward planarization approach, which computes a feasible upward planar subgraph in the first step and reinserts the remaining arcs by computing constraint-feasible upward insertion paths. An experimental study shows that the new algorithm leads to much better results than existing algorithms for upward crossing minimization, including the classical Sugiyama approach.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "Crossing number; planarization approach; upward drawing; upward planarization", } @Article{Bauer:2010:CHG, author = "Reinhard Bauer and Daniel Delling and Peter Sanders and Dennis Schieferdecker and Dominik Schultes and Dorothea Wagner", title = "Combining hierarchical and goal-directed speed-up techniques for {Dijkstra}'s algorithm", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "2.3:1--2.3:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1671976", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In recent years, highly effective hierarchical and goal-directed speed-up techniques for routing in large road networks have been developed. This article makes a systematic study of combinations of such techniques. These combinations turn out to give the best results in many scenarios, including graphs for unit disk graphs, grid networks, and time-expanded timetables. Besides these quantitative results, we obtain general insights for successful combinations.", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "Dijkstra's algorithm; speed-up technique", } @Article{Nash:2010:CID, author = "Nicholas Nash and David Gregg", title = "Comparing integer data structures for 32- and 64-bit keys", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "2.4:1--2.4:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1671977", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this article, we experimentally compare a number of data structures operating over keys that are 32- and 64-bit integers. We examine traditional comparison-based search trees as well as data structures that take advantage of the fact that the keys are integers such as van Emde Boas trees and various trie-based data structures. We propose a variant of a burst trie that performs better in time than all the alternative data structures. In addition, even for small sets of keys, this burst trie variant occupies less space than comparison-based data structures such as red-black trees and $B$-trees. Burst tries have previously been shown to provide a very efficient base for implementing cache efficient string sorting algorithms. We find that with suitable engineering, they also perform excellently as a dynamic ordered data structure operating over integer keys. We provide experimental results when the data structures operate over uniform random data. We also present experimental results for other types of data, including datasets arising from {\em Valgrind}, a widely used suite of tools for the dynamic binary instrumentation of programs.", acknowledgement = ack-nhfb, articleno = "2.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "Integer keys; level compression; searching; trees; tries", } @Article{Sinha:2010:EBT, author = "Ranjan Sinha and Anthony Wirth", title = "Engineering burstsort: Toward fast in-place string sorting", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "15", number = "1", pages = "2.5:1--2.5:??", month = mar, year = "2010", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1671970.1671978", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon Dec 10 09:03:03 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Burstsort is a trie-based string sorting algorithm that distributes strings into small buckets whose contents are then sorted in cache. This approach has earlier been demonstrated to be efficient on modern cache-based processors [Sinha \& Zobel, JEA 2004]. In this article, we introduce improvements that reduce by a significant margin the memory requirement of Burstsort: It is now less than 1\% greater than an in-place algorithm. These techniques can be applied to existing variants of Burstsort, as well as other string algorithms such as for string management.\par We redesigned the buckets, introducing sub-buckets and an index structure for them, which resulted in an order-of-magnitude space reduction. We also show the practicality of moving some fields from the trie nodes to the insertion point (for the next string pointer) in the bucket; this technique reduces memory usage of the trie nodes by one-third. Importantly, the trade-off for the reduction in memory use is only a very slight increase in the running time of Burstsort on real-world string collections. In addition, during the bucket-sorting phase, the string suffixes are copied to a small buffer to improve their spatial locality, lowering the running time of Burstsort by up to 30\%. These memory usage enhancements have enabled the copy-based approach [Sinha et al., JEA 2006] to also reduce the memory usage with negligible impact on speed.", acknowledgement = ack-nhfb, articleno = "2.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", keywords = "algorithms; cache; experimental algorithms; Sorting; string management; tries", } @Article{Boytsov:2011:IMA, author = "Leonid Boytsov", title = "Indexing methods for approximate dictionary searching: Comparative analysis", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "1.1:1--1.1:??", month = may, year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.1963191", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon May 30 08:26:05 MDT 2011", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The primary goal of this article is to survey state-of-the-art indexing methods for approximate dictionary searching. To improve understanding of the field, we introduce a taxonomy that classifies all methods into direct methods and sequence-based filtering methods. We focus on infrequently updated dictionaries, which are used primarily for retrieval. Therefore, we consider indices that are optimized for retrieval rather than for update. The indices are assumed to be associative, that is, capable of storing and retrieving auxiliary information, such as string identifiers. All solutions are lossless and guarantee retrieval of strings within a specified edit distance $k$. Benchmark results are presented for the practically important cases of $k = 1, 2$, and $3$.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Biro:2011:SMC, author = "P{\'e}ter Bir{\'o} and Robert W. Irving and Ildik{\'o} Schlotter", title = "Stable matching with couples: an empirical study", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "12:1--12:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.1970372", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In practical applications, algorithms for the classic version of the hospitals residents problem (the many-one version of the stable marriage problem) may have to be extended to accommodate the needs of couples who wish to be allocated to (geographically) compatible places. Such an extension has been in operation in the National Resident Matching Problem (NRMP) matching scheme in the United States for a number of years. In this setting, a stable matching need not exist, and it is an NP-complete problem to decide if one does. However, the only previous empirical study in this context (focused on the NRMP algorithm), together with information from NRMP, suggest that, in practice, stable matchings do exist and that an appropriate heuristic can be used to find such a matching. The study presented here was motivated by the recent decision to accommodate couples in the Scottish Foundation Allocation Scheme (SFAS), the Scottish equivalent of the NRMP. Here, the problem is a special case, since hospital preferences are derived from a ``master list'' of resident scores, but we show that the existence problem remains NP-complete in this case. We describe the algorithm used in SFAS and contrast it with a version of the algorithm that forms the basis of the NRMP approach. We also propose a third simpler algorithm based on satisfying blocking pairs, and an FPT algorithm when the number of couples is viewed as a parameter. We present an empirical study of the performance of a number of variants of these algorithms using a range of datasets. The results indicate that, not surprisingly, increasing the ratio of couples to single applicants typically makes it harder to find a stable matching (and, by inference, less likely that a stable matching exists). However, the likelihood of finding a stable matching is very high for realistic values of this ratio, and especially so for particular variants of the algorithms.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Huber:2011:MGS, author = "Stefan Huber and Martin Held", title = "Motorcycle graphs: Stochastic properties motivate an efficient yet simple implementation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "13:1--13:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2019578", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this article, we study stochastic properties of a geometric setting that underpins random motorcycle graphs and use it to motivate a simple but very efficient algorithm for computing motorcycle graphs. An analysis of the mean trace length of $n$ random motorcycles suggests that, on average, a motorcycle crosses only a constant number of cells within a $\sqrt n \times \sqrt n$ rectangular grid, provided that the motorcycles are distributed sufficiently uniformly over the area covered by the grid. This analysis motivates a simple algorithm for computing motorcycle graphs: We use the standard priority-queue--based algorithm and enhance it with geometric hashing by means of a rectangular grid. If the motorcycles are distributed sufficiently uniformly, then our stochastic analysis predicts an $O(n \log n)$ runtime. Indeed, extensive experiments run on 22,000 synthetic and real-world datasets confirm a runtime of less than $10^{-5} n \log n$ seconds for the vast majority of our datasets on a standard PC. Further experiments with our software, Moca, also confirm the mean trace length and average number of cells crossed by a motorcycle, as predicted by our analysis. This makes Moca the first implementation that is efficient enough to be applied in practice for computing motorcycle graphs of large datasets. Actually, it is easy to extend Moca to make it compute a generalized version of the original motorcycle graph, thus enabling a significantly larger field of applications.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Michail:2011:ECS, author = "Dimitrios Michail", title = "An experimental comparison of single-sided preference matching algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "14:1--14:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2019579", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We experimentally study the problem of assigning applicants to posts. Each applicant provides a preference list, which may contain ties, ranking a subset of the posts. Different optimization criteria may be defined, which depend on the desired solution properties. The main focus of this work is to assess the quality of matchings computed by rank-maximal and popular matching algorithms and compare this with the minimum weight matching algorithm, which is a standard matching algorithm that is used in practice. Both rank-maximal and popular matching algorithms use common algorithmic techniques, which makes them excellent candidates for a running time comparison. Since popular matchings do not always exist, we also study the unpopularity of matchings computed by the aforementioned algorithms. Finally, extra criteria like total weight and cardinality are included, due to their importance in practice. All experiments are performed using structured random instances as well as instances created using real-world datasets.", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Kot:2011:ECP, author = "Andriy Kot and Andrey N. Chernikov and Nikos P. Chrisochoides", title = "Effective out-of-core parallel {Delaunay} mesh refinement using off-the-shelf software", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "15:1--15:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2019580", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present three related out-of-core parallel mesh generation algorithms and their implementations for small size computational clusters. Computing out-of-core permits to solve larger problems than otherwise possible on the same hardware setup. Also, when using shared computing resources with high demand, a problem can take longer to compute in terms of wall-clock time when using an in-core algorithm on many nodes instead of using an out-of-core algorithm on few nodes. The difference is due to wait-in-queue delays that can grow exponentially to the number of requested nodes. In one specific case, using our best method and only 16 nodes it can take several times less wall-clock time to generate a 2 billion element mesh than to generate the same size mesh in-core with 121 nodes. Although our best out-of-core method exhibits unavoidable overheads (could be as low as 19\% in some cases) over the corresponding in-core method (for mesh sizes that fit completely in-core), this is a modest and expected performance penalty. We evaluated our methods on traditional clusters of workstations as well as presented preliminary performance evaluation on [the] emerging BlueWaters supercomputer.", acknowledgement = ack-nhfb, articleno = "1.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Prosser:2011:LDS, author = "Patrick Prosser and Chris Unsworth", title = "Limited discrepancy search revisited", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "16:1--16:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2019581", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Harvey and Ginsberg's limited discrepancy search (LDS) is based on the assumption that costly heuristic mistakes are made early in the search process. Consequently, LDS repeatedly probes the state space, going against the heuristic (i.e., taking discrepancies) a specified number of times in all possible ways and attempts to take those discrepancies as early as possible. LDS was improved by Richard Korf, to become improved LDS (ILDS), but in doing so, discrepancies were taken as late as possible, going against the original assumption. Many subsequent algorithms have faithfully inherited Korf's interpretation of LDS, and take discrepancies late. This then raises the question: Should we take our discrepancies late or early? We repeat the original experiments performed by Harvey and Ginsberg and those by Korf in an attempt to answer this question. We also investigate the early stopping condition of the YIELDS algorithm, demonstrating that it is simple, elegant and efficient.", acknowledgement = ack-nhfb, articleno = "1.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Tabourier:2011:GCR, author = "Lionel Tabourier and Camille Roth and Jean-Philippe Cointet", title = "Generating constrained random graphs using multiple edge switches", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "17:1--17:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2063515", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The generation of random graphs using edge swaps provides a reliable method to draw uniformly random samples of sets of graphs respecting some simple constraints (e.g., degree distributions). However, in general, it is not necessarily possible to access all graphs obeying some given constraints through a classical switching procedure calling on pairs of edges. Therefore, we propose to get around this issue by generalizing this classical approach through the use of higher-order edge switches. This method, which we denote by ``$k$-edge switching,'' makes it possible to progressively improve the covered portion of a set of constrained graphs, thereby providing an increasing, asymptotically certain confidence on the statistical representativeness of the obtained sample.", acknowledgement = ack-nhfb, articleno = "1.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Tsourakakis:2011:AAS, author = "Charalampos E. Tsourakakis and Richard Peng and Maria A. Tsiarli and Gary L. Miller and Russell Schwartz", title = "Approximation algorithms for speeding up dynamic programming and denoising {aCGH} data", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "18:1--18:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2063517", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The development of cancer is largely driven by the gain or loss of subsets of the genome, promoting uncontrolled growth or disabling defenses against it. Denoising array-based Comparative Genome Hybridization (aCGH) data is an important computational problem central to understanding cancer evolution. In this article, we propose a new formulation of the denoising problem that we solve with a ``vanilla'' dynamic programming algorithm, which runs in $O(n^2)$ units of time. Then, we propose two approximation techniques. Our first algorithm reduces the problem into a well-studied geometric problem, namely halfspace emptiness queries, and provides an $\epsilon$ additive approximation to the optimal objective value in $\tilde{O}(n ^{4 / 3 + \delta} \log (U / \epsilon))$ time, where $\delta$ is an arbitrarily small positive constant and $U = \max\{\sqrt C, (|P_i|)_{i = 1,\ldots{}, n}\} (P = (P_1, P_2, \ldots{}, P_n), P_i \in \mathbb{R})$, is the vector of the noisy aCGH measurements, $C$ a normalization constant. The second algorithm provides a $(1 \pm \epsilon)$ approximation (multiplicative error) and runs in $O(n \log n / \epsilon)$ time. The algorithm decomposes the initial problem into a small (logarithmic) number of Monge optimization subproblems that we can solve in linear time using existing techniques. Finally, we validate our model on synthetic and real cancer datasets. Our method consistently achieves superior precision and recall to leading competitors on the data with ground truth. In addition, it finds several novel markers not recorded in the benchmarks but supported in the oncology literature.", acknowledgement = ack-nhfb, articleno = "1.8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Vahrenhold:2011:P, author = "Jan Vahrenhold", title = "Preface", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "21:1--21:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.1970374", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Wang:2011:CEM, author = "Bei Wang and Herbert Edelsbrunner and Dmitriy Morozov", title = "Computing elevation maxima by searching the {Gauss} sphere", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "22:1--22:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.1970375", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The elevation function on a smoothly embedded 2-manifold in R$^3$ reflects the multiscale topography of cavities and protrusions as local maxima. The function has been useful in identifying coarse docking configurations for protein pairs. Transporting the concept from the smooth to the piecewise linear category, this article describes an algorithm for finding all local maxima. While its worst-case running time is the same as of the algorithm used in prior work, its performance in practice is orders of magnitudes superior. We cast light on this improvement by relating the running time to the total absolute Gaussian curvature of the 2-manifold.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Rotta:2011:MLS, author = "Randolf Rotta and Andreas Noack", title = "Multilevel local search algorithms for modularity clustering", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "23:1--23:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.1970376", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Modularity is a widely used quality measure for graph clusterings. Its exact maximization is NP-hard and prohibitively expensive for large graphs. Popular heuristics first perform a coarsening phase, where local search starting from singleton clusters is used to compute a preliminary clustering, and then optionally a refinement phase, where this clustering is improved by moving vertices between clusters. As a generalization, multilevel heuristics coarsen in several stages, and refine by moving entire clusters from each of these stages, not only individual vertices. This article organizes existing and new single-level and multilevel heuristics into a coherent design space, and compares them experimentally with respect to their effectiveness (achieved modularity) and runtime. For coarsening by iterated cluster joining, it turns out that the most widely used criterion for joining clusters (modularity increase) is outperformed by other simple criteria, that a recent multistep algorithm [Schuetz and Caflisch 2008] is no improvement over simple single-step coarsening for these criteria, and that the recent multilevel coarsening by iterated vertex moving [Blondel et al. 2008] is somewhat faster but slightly less effective (with refinement). The new multilevel refinement is significantly more effective than the conventional single-level refinement or no refinement, in reasonable runtime. A comparison with published benchmark results and algorithm implementations shows that multilevel local search heuristics, despite their relative simplicity, are competitive with the best algorithms in the literature.", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Bertasi:2011:PYA, author = "Paolo Bertasi and Marco Bressan and Enoch Peserico", title = "{{\tt psort}}, yet another fast stable sorting software", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "24:1--24:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.1970377", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "{\tt psort} is the fastest sorting software according to the PennySort benchmark, sorting 181GB of data in 2008 and 224GB in 2009 for \$0.01 of computer time. This article details its internals, and the careful fitting of its architecture to the structure of modern PC-class platforms, allowing it to outperform state-of-the-art sorting software such as STXXL sort.", acknowledgement = ack-nhfb, articleno = "2.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Finocchi:2011:GEF, author = "Irene Finocchi and John Hershberger", title = "Guest editors' foreword", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "31:1--31:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2025377", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "3.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Belazzougui:2011:TPM, author = "Djamal Belazzougui and Paolo Boldi and Rasmus Pagh and Sebastiano Vigna", title = "Theory and practice of monotone minimal perfect hashing", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "32:1--32:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2025378", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Minimal perfect hash functions have been shown to be useful to compress data in several data management tasks. In particular, order-preserving minimal perfect hash functions (Fox et al. 1991) have been used to retrieve the position of a key in a given list of keys; however, the ability to preserve any given order leads to an unavoidable $\Omega(n \log n)$ lower bound on the number of bits required to store the function. Recently, it was observed (Belazzougui et al. 2009) that very frequently the keys to be hashed are sorted in their intrinsic (i.e., lexicographical) order. This is typically the case of dictionaries of search engines, list of URLs of Web graphs, and so on. We refer to this restricted version of the problem as monotone minimal perfect hashing. We analyze experimentally the data structures proposed in Belazzougui et al. [2009], and along our way we propose some new methods that, albeit asymptotically equivalent or worse, perform very well in practice and provide a balance between access speed, ease of construction, and space usage.", acknowledgement = ack-nhfb, articleno = "3.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Doerr:2011:QRS, author = "Benjamin Doerr and Tobias Friedrich and Marvin K{\"u}nnemann and Thomas Sauerwald", title = "Quasirandom rumor spreading: an experimental analysis", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "33:1--33:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2025379", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We empirically analyze two versions of the well-known ``randomized rumor spreading'' protocol to disseminate a piece of information in networks. In the classical model, in each round, each informed node informs a random neighbor. In the recently proposed quasirandom variant, each node has a (cyclic) list of its neighbors. Once informed, it starts at a random position of the list, but from then on informs its neighbors in the order of the list. While for sparse random graphs a better performance of the quasirandom model could be proven, all other results show that, independent of the structure of the lists, the same asymptotic performance guarantees hold as for the classical model. In this work, we compare the two models experimentally. Not only does this show that the quasirandom model generally is faster, but it also shows that the runtime is more concentrated around the mean. This is surprising given that much fewer random bits are used in the quasirandom process. These advantages are also observed in a lossy communication model, where each transmission does not reach its target with a certain probability, and in an asynchronous model, where nodes send at random times drawn from an exponential distribution. We also show that typically the particular structure of the lists has little influence on the efficiency.", acknowledgement = ack-nhfb, articleno = "3.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Haverkort:2011:FDH, author = "Herman Haverkort and Freek V. Walderveen", title = "Four-dimensional {Hilbert} curves for {$R$}-trees", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "34:1--34:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2025380", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Two-dimensional R-trees are a class of spatial index structures in which objects are arranged to enable fast window queries: report all objects that intersect a given query window. One of the most successful methods of arranging the objects in the index structure is based on sorting the objects according to the positions of their centers along a two-dimensional Hilbert space-filling curve. Alternatively, one may use the coordinates of the objects' bounding boxes to represent each object by a four-dimensional point, and sort these points along a four-dimensional Hilbert-type curve. In experiments by Kamel and Faloutsos and by Arge et al., the first solution consistently outperformed the latter when applied to point data, while the latter solution clearly outperformed the first on certain artificial rectangle data. These authors did not specify which four-dimensional Hilbert-type curve was used; many exist. In this article, we show that the results of the previous articles can be explained by the choice of the four-dimensional Hilbert-type curve that was used and by the way it was rotated in four-dimensional space. By selecting a curve that has certain properties and choosing the right rotation, one can combine the strengths of the two-dimensional and the four-dimensional approach into one, while avoiding their apparent weaknesses. The effectiveness of our approach is demonstrated with experiments on various datasets. For real data taken from VLSI design, our new curve yields R-trees with query times that are better than those of R-trees that were obtained with previously used curves.", acknowledgement = ack-nhfb, articleno = "3.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Negrucseri:2011:SMF, author = "Cosmin Silvestru Negrucseri and Mircea Bogdan Pacsosi and Barbara Stanley and Clifford Stein and Cristian George Strat", title = "Solving maximum flow problems on real-world bipartite graphs", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "35:1--35:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2025381", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this article, we present an experimental study of several maximum-flow algorithms in the context of unbalanced bipartite networks. Our experiments are motivated by a real-world problem of managing reservation-based inventory in Google content ad systems. We are interested in observing the performance of several push-relabel algorithms on our real-world datasets and also on some generated ones. Previous work suggested an important improvement for push-relabel algorithms on unbalanced bipartite networks: the two-edge push rule. We show how the two-edge push rule improves the running time. While no single algorithm dominates the results, we show there is one that has very robust performance in practice.", acknowledgement = ack-nhfb, articleno = "3.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Tazari:2011:DLH, author = "Siamak Tazari and Matthias M{\"u}ller-Hannemann", title = "Dealing with large hidden constants: engineering a {Planar Steiner Tree (PTAS)}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "16", number = "1", pages = "36:1--36:??", year = "2011", CODEN = "????", DOI = "http://dx.doi.org/10.1145/1963190.2025382", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Sat Feb 25 18:02:18 MST 2012", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We present the first attempt on implementing a highly theoretical polynomial-time approximation scheme (PTAS) with huge hidden constants, namely, the PTAS for Steiner tree in planar graphs by Borradaile, Klein, and Mathieu (2009). Whereas this result, and several other PTAS results of the recent years, are of high theoretical importance, no practical applications or even implementation attempts have been known to date, due to the extremely large constants that are involved in them. We describe techniques on how to circumvent the challenges in implementing such a scheme. With today's limitations on processing power and space, we still have to sacrifice approximation guarantees for improved running times by choosing some parameters empirically. But our experiments show that with our choice of parameters, we do get the desired approximation ratios, suggesting that a much tighter analysis might be possible. Our computational experiments with benchmark instances from SteinLib and large artificial instances well exceeded our own expectations. We demonstrate that we are able to handle instances with up to a million nodes and several hundreds of terminals in 1.5 hours on a standard PC. On the rectilinear preprocessed instances from SteinLib, we observe a monotonous improvement for smaller values of $\epsilon$, with an average gap below 1\% for $\epsilon = 0.1$. We compare our implementation against the well-known batched $1$-Steiner heuristic and observe that on very large instances, we are able to produce comparable solutions much faster. We also present a thorough experimental evaluation of the influence of the various parameters of the PTAS and thus obtain a better understanding of their empirical effects.", acknowledgement = ack-nhfb, articleno = "3.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Reams:2012:AFD, author = "Charles Reams", title = "{Anatree}: a Fast Data Structure for Anagrams", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "17", number = "1", pages = "1.1:1--1.1:??", month = mar, year = "2012", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2133803.2133804", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jan 21 07:42:23 MST 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Natural language is a rich source of constraint satisfaction problems (CSPs), with a uniquely structured solution domain. We describe a number of approaches to satisfying the particular case of unordered letter-level constraints, including anagrams, but also relevant to typographical error correction, password security and word puzzles among other fields. We define the anatree, a data structure that can solve many such problems in constant time with respect to the size of the lexicon. The structure represents the lexicon of a language in a format somewhat analogous to a binary decision diagram (BDD) and, as with BDDs, construction heuristics allow the real average-case performance to vastly exceed the theoretical worst case. We compare anatrees and their alternatives empirically, explore the behavior of the construction heuristics, and characterize the tasks for which each is best suited.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Geisberger:2012:RPF, author = "Robert Geisberger and Michael N. Rice and Peter Sanders and Vassilis J. Tsotras", title = "Route planning with flexible edge restrictions", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "17", number = "1", pages = "1.2:1--1.2:??", month = mar, year = "2012", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2133803.2133805", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed Jan 21 07:42:23 MST 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this work, we explore a new type of flexible shortest-path query, in which the query can be dynamically parameterized to constrain the type of edges that may be included in the resulting shortest path (e.g., find the shortest path in a road network that avoids toll roads and low overpasses, respective of the specified vehicle height). We extend the hierarchical preprocessing technique known as Contraction Hierarchies to efficiently support such flexible queries. We also present several effective algorithmic optimizations for further improving the overall scalability and query times of this approach, including the addition of goal-directed search techniques, search space pruning techniques, and generalizing the constraints of the local search. Experiments are presented for both the North American and the European road networks, showcasing the general effectiveness and scalability of our proposed methodology to large-scale, real-world graphs.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Abraham:2013:ARR, author = "Ittai Abraham and Daniel Delling and Andrew V. Goldberg and Renato F. Werneck", title = "Alternative routes in road networks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "1.3:1--1.3:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2444019", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon May 6 18:55:51 MDT 2013", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study the problem of finding good alternative routes in road networks. We look for routes that are substantially different from the shortest path, have small stretch, and are locally optimal. We formally define the problem of finding alternative routes with a single via vertex, develop efficient algorithms for it, and evaluate them experimentally. Our algorithms are efficient enough for practical use and compare favorably with previous methods in both speed and solution quality.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Batz:2013:MTD, author = "G. Veit Batz and Robert Geisberger and Peter Sanders and Christian Vetter", title = "Minimum time-dependent travel times with contraction hierarchies", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "1.4:1--1.4:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2444020", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon May 6 18:55:51 MDT 2013", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Time-dependent road networks are represented as weighted graphs, where the weight of an edge depends on the time one passes through that edge. This way, we can model periodic congestions during rush hour and similar effects. In this work we deal with the special case where edge weights are time-dependent travel times. Namely, we consider two problems in this setting: Earliest arrival queries ask for a minimum travel time route for a start and a destination depending on a given departure time. Travel time profile queries ask for the travel time profile for a start, a destination, and an interval of possible departure times. For an instance representing the German road network, for example, we can answer earliest arrival queries in less than 1.5ms. For travel time profile queries, which are much harder to answer, we need less than 40ms if the interval of possible departure times has a width of 24 hours. For inexact travel time profiles with an allowed error of about 1\% this even reduces to 3.2ms. The underlying hierarchical representations of the road network, which are variants of a time-dependent contraction hierarchy (TCH), need less than 1GiB of space and can be generated in about 30 minutes. As far as we know, TCHs are currently the only method being able to answer travel time profile queries efficiently. Altogether, with TCHs, web servers with massive request traffic are able to provide fast time-dependent earliest arrival route planning and computation of travel time profiles.", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Bonami:2013:BRC, author = "Pierre Bonami and Jon Lee and Sven Leyffer and Andreas W{\"a}chter", title = "On branching rules for convex mixed-integer nonlinear optimization", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "2.6:1--2.6:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2532568", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Branch-and-Bound (B\&B) is perhaps the most fundamental algorithm for the global solution of convex Mixed-Integer Nonlinear Programming (MINLP) problems. It is well-known that carrying out branching in a nonsimplistic manner can greatly enhance the practicality of B\&B in the context of Mixed-Integer Linear Programming (MILP). No detailed study of branching has heretofore been carried out for MINLP. In this article, we study and identify useful sophisticated branching methods for MINLP, including novel approaches based on approximations of the nonlinear relaxations by linear and quadratic programs.", acknowledgement = ack-nhfb, articleno = "2.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Canzar:2013:PDA, author = "Stefan Canzar and Khaled Elbassioni and Juli{\'a}n Mestre", title = "A polynomial-delay algorithm for enumerating approximate solutions to the interval constrained coloring problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "2.2:1--2.2:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2493372", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study the interval constrained coloring problem, a combinatorial problem arising in the interpretation of data on protein structure emanating from experiments based on hydrogen/deuterium exchange and mass spectrometry. The problem captures the challenging task of increasing the spatial resolution of experimental data in order to get a better picture of the protein structure. Since solutions proposed by any algorithmic framework have to ultimately be verified by biochemists, it is important to provide not just a single solution, but a valuable set of candidate solutions. Our contribution is a polynomial-delay, polynomial-space algorithm for enumerating all exact solutions plus further approximate solutions, which are guaranteed to be within an absolute error of two of the optimum within fragments of the protein, that is, within sets of consecutive residues. Our experiments indicate that the quality of the approximate solutions is comparable to the optimal ones in terms of deviation from the underlying true solution. In addition, the experiments also confirm the effectiveness of the method in reducing the delay between two consecutive solutions considerably, compared to what it takes an integer programming solver to produce the next exact solution.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Delort:2013:HDP, author = "Charles Delort and Olivier Spanjaard", title = "A hybrid dynamic programming approach to the biobjective binary knapsack problem", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "1.2:1--1.2:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2444018", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "This article is devoted to a study of the impact of using bound sets in biobjective dynamic programming. This notion, introduced by Villareal and Karwan [1981], has been independently revisited by Ehrgott and Gandibleux [2007], as well as by Sourd and Spanjaard [2008]. The idea behind it is very general and can, therefore, be adapted to a wide range of biobjective combinatorial problems. We focus here on the biobjective binary knapsack problem. We show that using bound sets to perform a hybrid dynamic programming procedure embedded in a two-phase method [Ulungu and Teghem 1995] yields numerical results that outperform previous dynamic programming approaches to the problem, both in execution times and memory requirements.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Eppstein:2013:LAM, author = "David Eppstein and Maarten L{\"o}ffler and Darren Strash", title = "Listing All Maximal Cliques in Large Sparse Real-World Graphs", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "??", pages = "3.1:1--3.1:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2543629", ISSN = "1084-6654", bibdate = "Wed Jan 21 07:35:03 MST 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "3.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Ferraro-Petrillo:2013:DSR, author = "Umberto Ferraro-Petrillo and Fabrizio Grandoni and Giuseppe F. Italiano", title = "Data structures resilient to memory faults: an experimental study of dictionaries", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "1.6:1--1.6:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2444022", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon May 6 18:55:51 MDT 2013", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We address the problem of implementing data structures resilient to memory faults, which may arbitrarily corrupt memory locations. In this framework, we focus on the implementation of dictionaries and perform a thorough experimental study using a testbed that we designed for this purpose. Our main discovery is that the best-known (asymptotically optimal) resilient data structures have very large space overheads. More precisely, most of the space used by these data structures is not due to key storage. This might not be acceptable in practice, since resilient data structures are meant for applications where a huge amount of data (often of the order of terabytes) has to be stored. Exploiting techniques developed in the context of resilient (static) sorting and searching, in combination with some new ideas, we designed and engineered an alternative implementation, which, while still guaranteeing optimal asymptotic time and space bounds, performs much better in terms of memory without compromising the time efficiency.", acknowledgement = ack-nhfb, articleno = "1.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Festa:2013:FSI, author = "Paola Festa", title = "Foreword to the special issue {SEA 2010}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "1.1:1--1.1:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2444017", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Gog:2013:CST, author = "Simon Gog and Enno Ohlebusch", title = "Compressed suffix trees: Efficient computation and storage of {LCP}-values", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "2.1:1--2.1:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2461327", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The suffix tree is a very important data structure in string processing, but typical implementations suffer from huge space consumption. In large-scale applications, compressed suffix trees (CSTs) are therefore used instead. A CST consists of three (compressed) components: the suffix array, the longest common prefix (LCP)-array and data structures for simulating navigational operations on the suffix tree. The LCP-array stores the lengths of the LCPs of lexicographically adjacent suffixes, and it can be computed in linear time. In this article, we present a new LCP-array construction algorithm that is fast and very space efficient. In practice, our algorithm outperforms alternative algorithms. Moreover, we introduce a new compressed representation of LCP-arrays.", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Gorke:2013:DGC, author = "Robert G{\"o}rke and Pascal Maillard and Andrea Schumm and Christian Staudt and Dorothea Wagner", title = "Dynamic graph clustering combining modularity and smoothness", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "1.5:1--1.5:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2444021", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Mon May 6 18:55:51 MDT 2013", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Maximizing the quality index modularity has become one of the primary methods for identifying the clustering structure within a graph. Since many contemporary networks are not static but evolve over time, traditional static approaches can be inappropriate for specific tasks. In this work, we pioneer the NP-hard problem of online dynamic modularity maximization. We develop scalable dynamizations of the currently fastest and the most widespread static heuristics and engineer a heuristic dynamization of an optimal static algorithm. Our algorithms efficiently maintain a modularity -based clustering of a graph for which dynamic changes arrive as a stream. For our quickest heuristic we prove a tight bound on its number of operations. In an experimental evaluation on both a real-world dynamic network and on dynamic clustered random graphs, we show that the dynamic maintenance of a clustering of a changing graph yields higher modularity than recomputation, guarantees much smoother clustering dynamics, and requires much lower runtimes. We conclude with giving sound recommendations for the choice of an algorithm.", acknowledgement = ack-nhfb, articleno = "1.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Hofri:2013:OSS, author = "Micha Hofri", title = "Optimal selection and sorting via dynamic programming", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "2.3:1--2.3:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2444016.2493373", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We show how to find optimal algorithms for the selection of one or more order statistics over a small set of numbers, and as an extreme case, complete sorting. The criterion is using the smallest number of comparisons; separate derivations are performed for minimization on the average (over all permutations) or in the worst case. When the computational process establishes the optimal values, it also generates C-language functions that implement policies which achieve those optimal values. The search for the algorithms is driven by a Markov decision process, and the program provides the optimality proof as well.", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Kouri:2013:FRM, author = "Tina M. Kouri and Dinesh P. Mehta", title = "Faster reaction mapping through improved naming techniques", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "2.5:1--2.5:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2532569", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Automated reaction mapping is an important tool in cheminformatics where it may be used to classify reactions or validate reaction mechanisms. The reaction mapping problem is known to be NP-Hard and may be formulated as an optimization problem. In this article, we present four algorithms that continue to obtain optimal solutions to this problem, but with significantly improved runtimes over the previous Constructive Count Vector (CCV) algorithm. Our algorithmic improvements include (i) the use of a fast (but not 100\% accurate) canonical labeling algorithm, (ii) name reuse (i.e., storing intermediate results rather than recomputing), and (iii) an incremental approach to canonical name computation. The time to map the reactions from the Kegg/Ligand database previously took over 2 days using CCV, but now it takes fewer than 4 hours to complete. Experimental results on chemical reaction databases demonstrate our 2-CCV FDN MS algorithm usually performs over fifteen times faster than previous automated reaction mapping algorithms.", acknowledgement = ack-nhfb, articleno = "2.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Kouzinopoulos:2013:EOT, author = "Charalampos S. Kouzinopoulos and Konstantinos G. Margaritis", title = "Exact online two-dimensional pattern matching using multiple pattern matching algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "1", pages = "2.4:1--2.4:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2513148", ISSN = "1084-6654", ISSN-L = "1084-6654", bibdate = "Wed May 21 14:36:03 MDT 2014", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Baker and Bird and Baeza-Yates and Regnier are two of the most efficient and widely used algorithms for exact online two-dimensional pattern matching. Both use the automaton of the Aho--Corasick multiple pattern matching algorithm to locate all the occurrences of a two-dimensional pattern in a two-dimensional input string, a data structure that is considered by many as inefficient, especially when used to process long patterns or data using large alphabet sizes. This article presents variants of the Baker and Bird and the Baeza-Yates and Regnier algorithms that use the data structures of the Set Horspool, Wu-Manber, Set Backward Oracle Matching, and SOG multiple pattern matching algorithms in place of the automaton of Aho--Corasick and evaluates their performance experimentally in terms of preprocessing and searching time.", acknowledgement = ack-nhfb, articleno = "2.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Nagarajan:2013:EEI, author = "Chandrashekhar Nagarajan and David P. Williamson", title = "An Experimental Evaluation of Incremental and Hierarchical $k$-Median Algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "18", number = "??", pages = "3.2:1--3.2:??", month = dec, year = "2013", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2543628", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:23:43 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In this article, we consider different incremental and hierarchical $k$-median algorithms with provable performance guarantees and compare their running times and quality of output solutions on different benchmark $k$-median datasets. We determine that the quality of solutions output by these algorithms for all the datasets is much better than their performance guarantees suggest. Since some of the incremental $k$-median algorithms require approximate solutions for the $k$-median problem, we also compare some of the existing $k$-median algorithms running times and quality of solutions obtained on these datasets.", acknowledgement = ack-nhfb, articleno = "3.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Gonzalez:2015:LCS, author = "Rodrigo Gonz{\'a}lez and Gonzalo Navarro and H{\'e}ctor Ferrada", title = "Locally Compressed Suffix Arrays", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.1:1--1.1:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2594408", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/datacompression.bib; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We introduce a compression technique for suffix arrays. It is sensitive to the compressibility of the text and local, meaning that random portions of the suffix array can be decompressed by accessing mostly contiguous memory areas. This makes decompression very fast, especially when various contiguous cells must be accessed. Our main technical contributions are the following. First, we show that runs of consecutive values that are known to appear in function $ \Psi (i) = A^{-1} [A [i] + 1] $ of suffix arrays $A$ of compressible texts also show up as repetitions in the differential suffix array $ A'[i] = A [i] - A [i - 1]$. Second, we use Re-Pair, a grammar-based compressor, to compress the differential suffix array, and upper bound its compression ratio in terms of the number of runs. Third, we show how to compact the space used by the grammar rules by up to 50\%, while still permitting direct access to the rules. Fourth, we develop specific variants of Re-Pair that work using knowledge of $ \Psi $, and use much less space than the general Re-Pair compressor, while achieving almost the same compression ratios. Fifth, we implement the scheme and compare it exhaustively with previous work, including the first implementations of previous theoretical proposals.", acknowledgement = ack-nhfb, articleno = "1.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Doerr:2015:RRP, author = "Benjamin Doerr and Magnus Wahlstr{\"o}m", title = "Randomized Rounding in the Presence of a Cardinality Constraint", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.2:1--1.2:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2594409", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider the problem of generating randomized roundings that satisfy a single cardinality constraint and admit Chernoff-type large deviation bounds for weighted sums of the variables. That this can be done efficiently was proven by Srinivasan [2001], a different approach was later given by the first author [Doerr 2006]. In this work, we (a) present an improved version of the bitwise derandomization given by Doerr, (b) give the first derandomization of Srinivasan's tree-based randomized approach and prove its correctness, and (c) experimentally compare the resulting algorithms. Our experiments show that adding a single cardinality constraint typically reduces the rounding errors and only moderately increases the running times. In general, our derandomization of the tree-based approach is superior to the derandomized bitwise one, while the two randomized versions produce very similar rounding errors. When implementing the derandomized tree-based approach, however, the choice of the tree is important.", acknowledgement = ack-nhfb, articleno = "1.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Auer:2015:EMC, author = "B. O. Fagginger Auer and R. H. Bisseling", title = "Efficient Matching for Column Intersection Graphs", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.3:1--1.3:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2616587", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "To improve the quality and efficiency of hypergraph-based matrix partitioners, we investigate high-quality matchings in column intersection graphs of large sparse binary matrices. We show that such algorithms have a natural decomposition in an integer-weighted graph-matching function and a neighbor-finding function and study the performance of 16 combinations of these functions. We improve upon the original matching algorithm of the Mondriaan matrix partitioner: by using PGA', we improve the average matching quality from 95.3\% to 97.4\% of the optimum value; by using our new neighbor-finding heuristic, we obtain comparable quality and speedups of up to a factor of 19.6.", acknowledgement = ack-nhfb, articleno = "1.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Angione:2015:SMB, author = "Claudio Angione and Annalisa Occhipinti and Giuseppe Nicosia", title = "Satisfiability by {Maxwell--Boltzmann} and {Bose--Einstein} Statistical Distributions", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.4:1--1.4:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2629498", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Recent studies in theoretical computer science have exploited new algorithms and methodologies based on statistical physics for investigating the structure and the properties of the Satisfiability (SAT) problem. We propose a characterization of the SAT problem as a physical system, using both quantum and classical statistical-physical models. We associate a graph to an SAT instance and we prove that a Bose--Einstein condensation occurs in the instance with higher probability if the quantum distribution is adopted in the generation of the graph. Conversely, the fit-get-rich behavior is more likely if we adopt the Maxwell--Boltzmann distribution. Our method allows a comprehensive analysis of the SAT problem based on a new definition of entropy of an instance, without requiring the computation of its truth assignments. The entropy of an SAT instance increases in the satisfiability region as the number of free variables in the instance increases. Finally, we develop six new solvers for the MaxSAT problem based on quantum and classical statistical distributions, and we test them on random SAT instances, with competitive results. We experimentally prove that the performance of the solvers based on the two distributions depends on the criterion used to flag clauses as satisfied in the SAT solving process.", acknowledgement = ack-nhfb, articleno = "1.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Frieder:2015:ESA, author = "Asaf Frieder and Liam Roditty", title = "An Experimental Study on Approximating $k$ Shortest Simple Paths", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.5:1--1.5:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2630068", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We have conducted an extensive experimental study on approximation algorithms for computing $k$ shortest simple paths in weighted directed graphs. Very recently, Bernstein [2010] presented an algorithm that computes a $1 + \epsilon$ approximated $k$ shortest simple path in $O(\epsilon^{-1} k(m + n \log n) \log^2 n)$ time. We have implemented Bernstein's algorithm and tested it on synthetic inputs and real-world graphs (road maps). Our results reveal that Bernstein's algorithm has a practical value in many scenarios. Moreover, it produces in most of the cases exact paths rather than approximated. We also present a new variant for Bernstein's algorithm. We prove that our new variant has the same upper bounds for the running time and approximation as Bernstein's original algorithm. We have implemented and tested this variant as well. Our testing shows that this variant, which is based on a simple theoretical observation, is better than Bernstein's algorithm in practice.", acknowledgement = ack-nhfb, articleno = "1.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Gorke:2015:EDC, author = "Robert G{\"o}rke and Andrea Kappes and Dorothea Wagner", title = "Experiments on Density-Constrained Graph Clustering", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.6:1--1.6:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2638551", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Clustering a graph means identifying internally dense subgraphs that are only sparsely interconnected. Formalizations of this notion lead to measures that quantify the quality of a clustering and to algorithms that actually find clusterings. Since, most generally, corresponding optimization problems are hard, heuristic clustering algorithms are used in practice, or other approaches that are not based on an objective function. In this work, we conduct a comprehensive experimental evaluation of the qualitative behavior of greedy bottom-up heuristics driven by cut-based objectives and constrained by intracluster density, using both real-world data and artificial instances. Our study documents that a greedy strategy based on local movement is superior to one based on merging. We further reveal that the former approach generally outperforms alternative setups and reference algorithms from the literature in terms of its own objective, while a modularity-based algorithm competes surprisingly well. Finally, we exhibit which combinations of cut-based inter- and intracluster measures are suitable for identifying a hidden reference clustering in synthetic random graphs and discuss the skewness of the resulting cluster size distributions. Our results serve as a guideline to the usage of bicriterial, cut-based measures for graph clusterings.", acknowledgement = ack-nhfb, articleno = "1.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Galvao:2015:ATG, author = "Gustavo Rodrigues Galv{\~a}o and Zanoni Dias", title = "An Audit Tool for Genome Rearrangement Algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.7:1--1.7:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2661633", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider the combinatorial problem of sorting a permutation using a minimum number of rearrangement events, which finds application in the estimation of evolutionary distance between species. Many variants of this problem, which we generically refer to as the rearrangement sorting problem, have been tackled in the literature, and for most of them, the best known algorithms are approximations or heuristics. In this article, we present a tool, called GRAAu, to aid in the evaluation of the results produced by these algorithms. To illustrate its application, we use GRAAu to evaluate the results of four approximation algorithms regarding two variants of the rearrangement sorting problem: the problem of sorting by prefix reversals and the problem of sorting by prefix transpositions. As a result, we show that the approximation ratios of three algorithms are tight and conjecture that the approximation ratio of the remaining one is also tight.", acknowledgement = ack-nhfb, articleno = "1.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Grossi:2015:FCT, author = "Roberto Grossi and Giuseppe Ottaviano", title = "Fast Compressed Tries through Path Decompositions", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.8:1--1.8:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2656332", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/datacompression.bib; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Tries are popular data structures for storing a set of strings, where common prefixes are represented by common root-to-node paths. More than 50 years of usage have produced many variants and implementations to overcome some of their limitations. We explore new succinct representations of path-decomposed tries and experimentally evaluate the corresponding reduction in space usage and memory latency, comparing with the state of the art. We study the following applications: compressed string dictionary and monotone minimal perfect hash for strings. In compressed string dictionary, we obtain data structures that outperform other state-of-the-art compressed dictionaries in space efficiency while obtaining predictable query times that are competitive with data structures preferred by the practitioners. On real-world datasets, our compressed tries obtain the smallest space (except for one case) and have the fastest lookup times, whereas access times are within 20\% slower than the best-known solutions. In monotone minimal perfect hash for strings, our compressed tries perform several times faster than other trie-based monotone perfect hash functions while occupying nearly the same space. On real-world datasets, our tries are approximately 2 to 5 times faster than previous solutions, with a space occupancy less than 10\% larger.", acknowledgement = ack-nhfb, articleno = "1.8", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Jurkiewicz:2015:MVA, author = "Tomasz Jurkiewicz and Kurt Mehlhorn", title = "On a Model of Virtual Address Translation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "1.9:1--1.9:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2656337", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Modern computers are not Random Access Machines (RAMs). They have a memory hierarchy, multiple cores, and a virtual memory. We address the computational cost of the address translation in the virtual memory. The starting point for our work on virtual memory is the observation that the analysis of some simple algorithms (random scan of an array, binary search, heapsort) in either the RAM model or the External Memory (EM) model does not correctly predict growth rates of actual running times. We propose the Virtual Address Translation (VAT) model to account for the cost of address translations and analyze the algorithms mentioned and others in the model. The predictions agree with the measurements. We also analyze the VAT-cost of cache-oblivious algorithms.", acknowledgement = ack-nhfb, articleno = "1.9", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Klasing:2015:E, author = "Ralf Klasing", title = "Editorial", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "2.1:1--2.1:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2677196", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "2.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Safro:2015:ACS, author = "Ilya Safro and Peter Sanders and Christian Schulz", title = "Advanced Coarsening Schemes for Graph Partitioning", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "2.2:1--2.2:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2670338", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "The graph partitioning problem is widely used and studied in many practical and theoretical applications. Today, multilevel strategies represent one of the most effective and efficient generic frameworks for solving this problem on large-scale graphs. Most of the attention in designing multilevel partitioning frameworks has been on the refinement phase. In this work, we focus on the coarsening phase, which is responsible for creating structures similar to the original but smaller graphs. We compare different matching- and AMG-based coarsening schemes, experiment with the algebraic distance between nodes, and demonstrate computational results on several classes of graphs that emphasize the running time and quality advantages of different coarsening schemes.", acknowledgement = ack-nhfb, articleno = "2.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Navarro:2015:GDR, author = "Gonzalo Navarro and Simon J. Puglisi and Daniel Valenzuela", title = "General Document Retrieval in Compact Space", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "2.3:1--2.3:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2670128", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/datacompression.bib; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "Given a collection of documents and a query pattern, document retrieval is the problem of obtaining documents that are relevant to the query. The collection is available beforehand so that a data structure, called an index, can be built on it to speed up queries. While initially restricted to natural language text collections, document retrieval problems arise nowadays in applications like bioinformatics, multimedia databases, and web mining. This requires a more general setup where text and pattern can be general sequences of symbols, and the classical inverted indexes developed for words cannot be applied. While linear-space time-optimal solutions have been developed for most interesting queries in this general case, space usage is a serious problem in practice. In this article, we develop compact data structures that solve various important document retrieval problems on general text collections. More specifically, we provide practical solutions for listing the documents where a query pattern appears, together with its frequency in each document, and for listing $k$ documents where a query pattern appears most frequently. Some of our techniques build on existing theoretical proposals, while others are new. In particular, we introduce a novel grammar-based compressed bitmap representation that may be of independent interest when dealing with repetitive sequences. Ours are the first practical indexes that use less space when the text collection is compressible. Our experimental results show that, in various real-life text collections, our data structures are significantly smaller than the most space-efficient previous solutions, using up to half the space without noticeably increasing the query time. Overall, document listing can be carried out in 10 to 40 milliseconds for patterns that appear 100 to 10,000 times in the collection, whereas top-$k$ retrieval is carried out in $k$ to $ 10 k$ milliseconds.", acknowledgement = ack-nhfb, articleno = "2.3", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Moruz:2015:EEP, author = "Gabriel Moruz and Andrei Negoescu and Christian Neumann and Volker Weichert", title = "Engineering Efficient Paging Algorithms", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "2.4:1--2.4:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2670127", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In the field of online algorithms, paging is a well-studied problem. LRU is a simple paging algorithm that incurs few cache misses and supports efficient implementations. Algorithms outperforming LRU in terms of cache misses exist but are in general more complex and thus not automatically better, since their increased runtime might annihilate the gains in cache misses. In this article, we focus on efficient implementations for the O nOPT class described in Moruz and Negoescu [2012], particularly on an algorithm in this class, denoted RDM, that was shown to typically incur fewer misses than LRU. We provide experimental evidence on a wide range of cache traces showing that our implementation of RDM is competitive to LRU with respect to runtime. In a scenario incurring realistic time penalties for cache misses, we show that our implementation consistently outperforms LRU, even if the runtime of LRU is set to zero.", acknowledgement = ack-nhfb, articleno = "2.4", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Kirchler:2015:ECS, author = "Dominik Kirchler and Leo Liberti and Roberto Wolfler Calvo", title = "Efficient Computation of Shortest Paths in Time-Dependent Multi-Modal Networks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "2.5:1--2.5:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2670126", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We consider shortest paths on time-dependent multimodal transportation networks in which restrictions or preferences on the use of certain modes of transportation may arise. We model restrictions and preferences by means of regular languages. Methods for solving the corresponding problem (called the regular language constrained shortest path problem ) already exist. We propose a new algorithm, called State Dependent ALT (SDALT), which runs considerably faster in many scenarios. Speed-up magnitude depends on the type of constraints. We present different versions of SDALT, including unidirectional and bidirectional search. We also provide extensive experimental results on realistic multimodal transportation networks.", acknowledgement = ack-nhfb, articleno = "2.5", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Manlove:2015:PAK, author = "David F. Manlove and Gregg O'malley", title = "Paired and Altruistic Kidney Donation in the {UK}: Algorithms and Experimentation", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "2.6:1--2.6:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2670129", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study the computational problem of identifying optimal sets of kidney exchanges in the UK. We show how to expand an integer programming-based formulation due to Roth et al. [2007] in order to model the criteria that constitute the UK definition of optimality. The software arising from this work has been used by the National Health Service Blood and Transplant to find optimal sets of kidney exchanges for their National Living Donor Kidney Sharing Schemes since July 2008. We report on the characteristics of the solutions that have been obtained in matching runs of the scheme since this time. We then present empirical results arising from experiments on the real datasets that stem from these matching runs, with the aim of establishing the extent to which the particular optimality criteria that are present in the UK influence the structure of the solutions that are ultimately computed. A key observation is that allowing four-way exchanges would be likely to lead to a moderate number of additional transplants.", acknowledgement = ack-nhfb, articleno = "2.6", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Luxen:2015:CSA, author = "Dennis Luxen and Dennis Schieferdecker", title = "Candidate Sets for Alternative Routes in Road Networks", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "2.7:1--2.7:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2674395", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "We study the computation of good alternatives to the shortest path in road networks. Our approach is based on single via-node routing on top of contraction hierarchies and achieves superior quality and efficiency compared to previous methods. We present a fast preprocessing method for computing multiple good alternatives and apply this result in an online setting. This setting makes our result applicable in legacy systems with negligible memory overhead. An extensive experimental analysis on a continental-sized real- world road network proves the performance of our algorithm and supports the general systematic algorithm engineering approach. We also show how to combine our results with the competing concept of alternative graphs that encode many alternative paths at once.", acknowledgement = ack-nhfb, articleno = "2.7", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Bader:2015:ISI, author = "David A. Bader and Petra Mutzel", title = "Introduction to Special Issue {ALENEX'12}", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "3.1:1--3.1:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2721893", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", acknowledgement = ack-nhfb, articleno = "3.1", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", } @Article{Dibbelt:2015:UCM, author = "Julian Dibbelt and Thomas Pajor and Dorothea Wagner", title = "User-Constrained Multimodal Route Planning", journal = j-ACM-J-EXP-ALGORITHMICS, volume = "19", number = "??", pages = "3.2:1--3.2:??", month = feb, year = "2015", CODEN = "????", DOI = "http://dx.doi.org/10.1145/2699886", ISSN = "1084-6654", bibdate = "Fri Apr 3 16:22:03 MDT 2015", bibsource = "http://portal.acm.org/; http://www.math.utah.edu/pub/tex/bib/jea.bib", abstract = "In the multimodal route planning problem, we are given multiple transportation networks (e.g., pedestrian, road, public transit) and ask for a best integrated journey between two points. The main challenge is that a seemingly optimal journey may have changes between networks that do not reflect the user's modal preferences. In fact, quickly computing reasonable multimodal routes remains a challenging problem: previous approaches either suffer from poor query performance or their available choices of modal preferences during query time is limited. In this work, we focus on computing exact multimodal journeys that can be restricted by specifying arbitrary modal sequences at query time. For example, a user can say whether he or she wants to only use public transit, prefers to also use a taxi or walking at the beginning or end of the journey, or has no restrictions at all. By carefully adapting node contraction, a common ingredient to many speedup techniques on road networks, we are able to compute point-to-point queries on a continental network combined of cars, railroads, and flights several orders of magnitude faster than Dijkstra's algorithm. Thereby, we require little space overhead and obtain fast preprocessing times.", acknowledgement = ack-nhfb, articleno = "3.2", fjournal = "Journal of Experimental Algorithmics (JEA)", journal-URL = "http://portal.acm.org/browse_dl.cfm?idx=J430", }