subroutine odrv
* (n, ia,ja,a, p,ip, nsp,isp, path, flag)
clll. optimize
c 5/2/83
c***********************************************************************
c odrv -- driver for sparse matrix reordering routines
c***********************************************************************
c
c description
c
c odrv finds a minimum degree ordering of the rows and columns
c of a matrix m stored in (ia,ja,a) format (see below). for the
c reordered matrix, the work and storage required to perform
c gaussian elimination is (usually) significantly less.
c
c note.. odrv and its subordinate routines have been modified to
c compute orderings for general matrices, not necessarily having any
c symmetry. the miminum degree ordering is computed for the
c structure of the symmetric matrix m + m-transpose.
c modifications to the original odrv module have been made in
c the coding in subroutine mdi, and in the initial comments in
c subroutines odrv and md.
c
c if only the nonzero entries in the upper triangle of m are being
c stored, then odrv symmetrically reorders (ia,ja,a), (optionally)
c with the diagonal entries placed first in each row. this is to
c ensure that if m(i,j) will be in the upper triangle of m with
c respect to the new ordering, then m(i,j) is stored in row i (and
c thus m(j,i) is not stored), whereas if m(i,j) will be in the
c strict lower triangle of m, then m(j,i) is stored in row j (and
c thus m(i,j) is not stored).
c
c
c storage of sparse matrices
c
c the nonzero entries of the matrix m are stored row-by-row in the
c array a. to identify the individual nonzero entries in each row,
c we need to know in which column each entry lies. these column
c indices are stored in the array ja. i.e., if a(k) = m(i,j), then
c ja(k) = j. to identify the individual rows, we need to know where
c each row starts. these row pointers are stored in the array ia.
c i.e., if m(i,j) is the first nonzero entry (stored) in the i-th row
c and a(k) = m(i,j), then ia(i) = k. moreover, ia(n+1) points to
c the first location following the last element in the last row.
c thus, the number of entries in the i-th row is ia(i+1) - ia(i),
c the nonzero entries in the i-th row are stored consecutively in
c
c a(ia(i)), a(ia(i)+1), ..., a(ia(i+1)-1),
c
c and the corresponding column indices are stored consecutively in
c
c ja(ia(i)), ja(ia(i)+1), ..., ja(ia(i+1)-1).
c
c since the coefficient matrix is symmetric, only the nonzero entries
c in the upper triangle need be stored. for example, the matrix
c
c ( 1 0 2 3 0 )
c ( 0 4 0 0 0 )
c m = ( 2 0 5 6 0 )
c ( 3 0 6 7 8 )
c ( 0 0 0 8 9 )
c
c could be stored as
c
c - 1 2 3 4 5 6 7 8 9 10 11 12 13
c ---+--------------------------------------
c ia - 1 4 5 8 12 14
c ja - 1 3 4 2 1 3 4 1 3 4 5 4 5
c a - 1 2 3 4 2 5 6 3 6 7 8 8 9
c
c or (symmetrically) as
c
c - 1 2 3 4 5 6 7 8 9
c ---+--------------------------
c ia - 1 4 5 7 9 10
c ja - 1 3 4 2 3 4 4 5 5
c a - 1 2 3 4 5 6 7 8 9 .
c
c
c parameters
c
c n - order of the matrix
c
c ia - integer one-dimensional array containing pointers to delimit
c rows in ja and a. dimension = n+1
c
c ja - integer one-dimensional array containing the column indices
c corresponding to the elements of a. dimension = number of
c nonzero entries in (the upper triangle of) m
c
c a - real one-dimensional array containing the nonzero entries in
c (the upper triangle of) m, stored by rows. dimension =
c number of nonzero entries in (the upper triangle of) m
c
c p - integer one-dimensional array used to return the permutation
c of the rows and columns of m corresponding to the minimum
c degree ordering. dimension = n
c
c ip - integer one-dimensional array used to return the inverse of
c the permutation returned in p. dimension = n
c
c nsp - declared dimension of the one-dimensional array isp. nsp
c must be at least 3n+4k, where k is the number of nonzeroes
c in the strict upper triangle of m
c
c isp - integer one-dimensional array used for working storage.
c dimension = nsp
c
c path - integer path specification. values and their meanings are -
c 1 find minimum degree ordering only
c 2 find minimum degree ordering and reorder symmetrically
c stored matrix (used when only the nonzero entries in
c the upper triangle of m are being stored)
c 3 reorder symmetrically stored matrix as specified by
c input permutation (used when an ordering has already
c been determined and only the nonzero entries in the
c upper triangle of m are being stored)
c 4 same as 2 but put diagonal entries at start of each row
c 5 same as 3 but put diagonal entries at start of each row
c
c flag - integer error flag. values and their meanings are -
c 0 no errors detected
c 9n+k insufficient storage in md
c 10n+1 insufficient storage in odrv
c 11n+1 illegal path specification
c
c
c conversion from real to double precision
c
c change the real declarations in odrv and sro to double precision
c declarations.
c
c-----------------------------------------------------------------------
c
integer ia(1), ja(1), p(1), ip(1), isp(1), path, flag,
* v, l, head, tmp, q
double precision a(1)
logical dflag
c
c----initialize error flag and validate path specification
flag = 0
if (path.lt.1 .or. 5.lt.path) go to 111
c
c----allocate storage and find minimum degree ordering
if ((path-1) * (path-2) * (path-4) .ne. 0) go to 1
max = (nsp-n)/2
v = 1
l = v + max
head = l + max
next = head + n
if (max.lt.n) go to 110
c
call md
* (n, ia,ja, max,isp(v),isp(l), isp(head),p,ip, isp(v), flag)
if (flag.ne.0) go to 100
c
c----allocate storage and symmetrically reorder matrix
1 if ((path-2) * (path-3) * (path-4) * (path-5) .ne. 0) go to 2
tmp = (nsp+1) - n
q = tmp - (ia(n+1)-1)
if (q.lt.1) go to 110
c
dflag = path.eq.4 .or. path.eq.5
call sro
* (n, ip, ia, ja, a, isp(tmp), isp(q), dflag)
c
2 return
c
c ** error -- error detected in md
100 return
c ** error -- insufficient storage
110 flag = 10*n + 1
return
c ** error -- illegal path specified
111 flag = 11*n + 1
return
end