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slasdt.f
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1 *> \brief \b SLASDT creates a tree of subproblems for bidiagonal divide and conquer. Used by sbdsdc.
2 *
3 * =========== DOCUMENTATION ===========
4 *
5 * Online html documentation available at
6 * http://www.netlib.org/lapack/explore-html/
7 *
8 *> \htmlonly
9 *> Download SLASDT + dependencies
10 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.tgz?format=tgz&filename=/lapack/lapack_routine/slasdt.f">
11 *> [TGZ]</a>
12 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.zip?format=zip&filename=/lapack/lapack_routine/slasdt.f">
13 *> [ZIP]</a>
14 *> <a href="http://www.netlib.org/cgi-bin/netlibfiles.txt?format=txt&filename=/lapack/lapack_routine/slasdt.f">
15 *> [TXT]</a>
16 *> \endhtmlonly
17 *
18 * Definition:
19 * ===========
20 *
21 * SUBROUTINE SLASDT( N, LVL, ND, INODE, NDIML, NDIMR, MSUB )
22 *
23 * .. Scalar Arguments ..
24 * INTEGER LVL, MSUB, N, ND
25 * ..
26 * .. Array Arguments ..
27 * INTEGER INODE( * ), NDIML( * ), NDIMR( * )
28 * ..
29 *
30 *
31 *> \par Purpose:
32 * =============
33 *>
34 *> \verbatim
35 *>
36 *> SLASDT creates a tree of subproblems for bidiagonal divide and
37 *> conquer.
38 *> \endverbatim
39 *
40 * Arguments:
41 * ==========
42 *
43 *> \param[in] N
44 *> \verbatim
45 *> N is INTEGER
46 *> On entry, the number of diagonal elements of the
47 *> bidiagonal matrix.
48 *> \endverbatim
49 *>
50 *> \param[out] LVL
51 *> \verbatim
52 *> LVL is INTEGER
53 *> On exit, the number of levels on the computation tree.
54 *> \endverbatim
55 *>
56 *> \param[out] ND
57 *> \verbatim
58 *> ND is INTEGER
59 *> On exit, the number of nodes on the tree.
60 *> \endverbatim
61 *>
62 *> \param[out] INODE
63 *> \verbatim
64 *> INODE is INTEGER array, dimension ( N )
65 *> On exit, centers of subproblems.
66 *> \endverbatim
67 *>
68 *> \param[out] NDIML
69 *> \verbatim
70 *> NDIML is INTEGER array, dimension ( N )
71 *> On exit, row dimensions of left children.
72 *> \endverbatim
73 *>
74 *> \param[out] NDIMR
75 *> \verbatim
76 *> NDIMR is INTEGER array, dimension ( N )
77 *> On exit, row dimensions of right children.
78 *> \endverbatim
79 *>
80 *> \param[in] MSUB
81 *> \verbatim
82 *> MSUB is INTEGER
83 *> On entry, the maximum row dimension each subproblem at the
84 *> bottom of the tree can be of.
85 *> \endverbatim
86 *
87 * Authors:
88 * ========
89 *
90 *> \author Univ. of Tennessee
91 *> \author Univ. of California Berkeley
92 *> \author Univ. of Colorado Denver
93 *> \author NAG Ltd.
94 *
95 *> \date September 2012
96 *
97 *> \ingroup auxOTHERauxiliary
98 *
99 *> \par Contributors:
100 * ==================
101 *>
102 *> Ming Gu and Huan Ren, Computer Science Division, University of
103 *> California at Berkeley, USA
104 *>
105 * =====================================================================
106  SUBROUTINE slasdt( N, LVL, ND, INODE, NDIML, NDIMR, MSUB )
107 *
108 * -- LAPACK auxiliary routine (version 3.4.2) --
109 * -- LAPACK is a software package provided by Univ. of Tennessee, --
110 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
111 * September 2012
112 *
113 * .. Scalar Arguments ..
114  INTEGER lvl, msub, n, nd
115 * ..
116 * .. Array Arguments ..
117  INTEGER inode( * ), ndiml( * ), ndimr( * )
118 * ..
119 *
120 * =====================================================================
121 *
122 * .. Parameters ..
123  REAL two
124  parameter( two = 2.0e+0 )
125 * ..
126 * .. Local Scalars ..
127  INTEGER i, il, ir, llst, maxn, ncrnt, nlvl
128  REAL temp
129 * ..
130 * .. Intrinsic Functions ..
131  INTRINSIC int, log, max, real
132 * ..
133 * .. Executable Statements ..
134 *
135 * Find the number of levels on the tree.
136 *
137  maxn = max( 1, n )
138  temp = log( REAL( MAXN ) / REAL( MSUB+1 ) ) / log( two )
139  lvl = int( temp ) + 1
140 *
141  i = n / 2
142  inode( 1 ) = i + 1
143  ndiml( 1 ) = i
144  ndimr( 1 ) = n - i - 1
145  il = 0
146  ir = 1
147  llst = 1
148  DO 20 nlvl = 1, lvl - 1
149 *
150 * Constructing the tree at (NLVL+1)-st level. The number of
151 * nodes created on this level is LLST * 2.
152 *
153  DO 10 i = 0, llst - 1
154  il = il + 2
155  ir = ir + 2
156  ncrnt = llst + i
157  ndiml( il ) = ndiml( ncrnt ) / 2
158  ndimr( il ) = ndiml( ncrnt ) - ndiml( il ) - 1
159  inode( il ) = inode( ncrnt ) - ndimr( il ) - 1
160  ndiml( ir ) = ndimr( ncrnt ) / 2
161  ndimr( ir ) = ndimr( ncrnt ) - ndiml( ir ) - 1
162  inode( ir ) = inode( ncrnt ) + ndiml( ir ) + 1
163  10 CONTINUE
164  llst = llst*2
165  20 CONTINUE
166  nd = llst*2 - 1
167 *
168  RETURN
169 *
170 * End of SLASDT
171 *
172  END