odrv(3f) [M_odepack] - driver for sparse matrix reordering routines
odrv finds a minimum degree ordering of the rows and columns of a matrix m stored in (ia,ja,a) format (see below). for the reordered matrix, the work and storage required to perform gaussian elimination is (usually) significantly less.
note.. odrv and its subordinate routines have been modified to compute orderings for general matrices, not necessarily having any symmetry. the miminum degree ordering is computed for the structure of the symmetric matrix m + m-transpose. modifications to the original odrv module have been made in the coding in subroutine mdi, and in the initial comments in subroutines odrv and md.
if only the nonzero entries in the upper triangle of m are being stored, then odrv symmetrically reorders (ia,ja,a), (optionally) with the diagonal entries placed first in each row. this is to ensure that if m(i,j) will be in the upper triangle of m with respect to the new ordering, then m(i,j) is stored in row i (and thus m(j,i) is not stored), whereas if m(i,j) will be in the strict lower triangle of m, then m(j,i) is stored in row j (and thus m(i,j) is not stored).
the nonzero entries of the matrix m are stored row-by-row in the array a. to identify the individual nonzero entries in each row, we need to know in which column each entry lies. these column indices are stored in the array ja. i.e., if a(k) = m(i,j), then ja(k) = j. to identify the individual rows, we need to know where each row starts. these row pointers are stored in the array ia. i.e., if m(i,j) is the first nonzero entry (stored) in the i-th row and a(k) = m(i,j), then ia(i) = k. moreover, ia(n+1) points to the first location following the last element in the last row. thus, the number of entries in the i-th row is ia(i+1) - ia(i), the nonzero entries in the i-th row are stored consecutively in
a(ia(i)), a(ia(i)+1), ..., a(ia(i+1)-1),
and the corresponding column indices are stored consecutively in
ja(ia(i)), ja(ia(i)+1), ..., ja(ia(i+1)-1).
when the coefficient matrix is symmetric, only the nonzero entries in the upper triangle need be stored. for example, the matrix
( 1 0 2 3 0 )
( 0 4 0 0 0 )
m = ( 2 0 5 6 0 )
( 3 0 6 7 8 )
( 0 0 0 8 9 )
could be stored as
- 1 2 3 4 5 6 7 8 9 10 11 12 13
---+--------------------------------------
ia - 1 4 5 8 12 14
ja - 1 3 4 2 1 3 4 1 3 4 5 4 5
a - 1 2 3 4 2 5 6 3 6 7 8 8 9
or (symmetrically) as
- 1 2 3 4 5 6 7 8 9
---+--------------------------
ia - 1 4 5 7 9 10
ja - 1 3 4 2 3 4 4 5 5
a - 1 2 3 4 5 6 7 8 9 .
n - order of the matrix
ia - integer one-dimensional array containing pointers to delimit
rows in ja and a. dimension = n+1
ja - integer one-dimensional array containing the column indices
corresponding to the elements of a. dimension = number of
nonzero entries in (the upper triangle of) m
a - real one-dimensional array containing the nonzero entries in
(the upper triangle of) m, stored by rows. dimension =
number of nonzero entries in (the upper triangle of) m
p - integer one-dimensional array used to return the permutation
of the rows and columns of m corresponding to the minimum
degree ordering. dimension = n
ip - integer one-dimensional array used to return the inverse of
the permutation returned in p. dimension = n
nsp - declared dimension of the one-dimensional array isp. nsp
must be at least 3n+4k, where k is the number of nonzeroes
in the strict upper triangle of m
isp - integer one-dimensional array used for working storage.
dimension = nsp
path - integer path specification. values and their meanings are -
1 find minimum degree ordering only
2 find minimum degree ordering and reorder symmetrically
stored matrix (used when only the nonzero entries in
the upper triangle of m are being stored)
3 reorder symmetrically stored matrix as specified by
input permutation (used when an ordering has already
been determined and only the nonzero entries in the
upper triangle of m are being stored)
4 same as 2 but put diagonal entries at start of each row
5 same as 3 but put diagonal entries at start of each row
flag - integer error flag. values and their meanings are -
0 no errors detected
9n+k insufficient storage in md
10n+1 insufficient storage in odrv
11n+1 illegal path specification
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| integer | :: | N | ||||
| integer, | dimension(*) | :: | Ia | |||
| integer, | dimension(*) | :: | Ja | |||
| real(kind=dp), | dimension(*) | :: | A | |||
| integer, | dimension(*) | :: | P | |||
| integer, | dimension(*) | :: | Ip | |||
| integer, | intent(in) | :: | Nsp | |||
| integer, | dimension(*) | :: | Isp | |||
| integer, | intent(in) | :: | Path | |||
| integer, | intent(inout) | :: | Flag |