HP MLIB User's Guide Vol. 2 7th Ed.

1036 HP MLIB User’s Guide
DSEVEX Eigenextraction
Name DSEVEX
Eigenextraction
Purpose This subprogram computes selected eigenvalues and eigenvectors of a sparse
symmetric matrix A or of a sparse symmetric matrix pencil (A,B). The matrix or
matrices have already been processed through the structure input, reordering,
and value input phases. This is the sophisticated interface; subroutine
DSEVES is simpler to use.
DSEVEX allows the user to control three parameters, the block size, the
accuracy tolerance, and the shifting scale, that are selected heuristically by
DSEVE1. DSEVEX also provides a mechanism for giving initial guesses for the
eigenvectors. Each of these parameters is described in more detail in “Usage”.
Users with a great deal of experience in particular applications may find more
efficient settings for these parameters than the general defaults in the code.
However, it should be noted that the performance of the package can be
degraded significantly by poor choices.
Usage VECLIB:
CHARACTER*1 which, pbtype
INTEGER*4 neigvl, mxbksz, nusrvc, nfound, ndiscd, ier, warnng
LOGICAL*4 lfinit, rfinit
REAL*8 lftend, rhtend, center, tolact, shfscl, global(150),
usrsvc(norder, nusrvc)
CALL DSEVEX(neigvl, which, pbtype, lfinit, lftend, rfinit, rhtend,
center, mxbksz, tolact, shfscl, nusrvc, usrsvc, nfound, ndiscd, global, ier,
warnng)
VECLIB8:
CHARACTER*1 which, pbtype
INTEGER*8 neigvl, mxbksz, nusrvc, nfound, ndiscd, ier, warnng
LOGICAL*4 lfinit, rfinit
REAL*8 lftend, rhtend, center, tolact, shfscl, global(150),
usrsvc(norder, nusrvc)
CALL DSEVEX(neigvl, which, pbtype, lfinit, lftend, rfinit, rhtend,
center, mxbksz, tolact, shfscl, nusrvc, usrsvc, nfound, ndiscd, global, ier,
warnng)
Input neigvl Number of eigenvalues to be found.
which Character string indicating which eigenvalues are to be
computed:
’L’ or ’l’ The lowest (smallest magnitude)
eigenvalues.