dggbak(3P) Sun Performance Library dggbak(3P)NAMEdggbak - form the right or left eigenvectors of a real generalized ei‐
genvalue problem A*x = lambda*B*x, by backward transformation on the
computed eigenvectors of the balanced pair of matrices output by DGGBAL
SYNOPSIS
SUBROUTINE DGGBAK(JOB, SIDE, N, ILO, IHI, LSCALE, RSCALE, M, V, LDV,
INFO)
CHARACTER * 1 JOB, SIDE
INTEGER N, ILO, IHI, M, LDV, INFO
DOUBLE PRECISION LSCALE(*), RSCALE(*), V(LDV,*)
SUBROUTINE DGGBAK_64(JOB, SIDE, N, ILO, IHI, LSCALE, RSCALE, M, V,
LDV, INFO)
CHARACTER * 1 JOB, SIDE
INTEGER*8 N, ILO, IHI, M, LDV, INFO
DOUBLE PRECISION LSCALE(*), RSCALE(*), V(LDV,*)
F95 INTERFACE
SUBROUTINE GGBAK(JOB, SIDE, [N], ILO, IHI, LSCALE, RSCALE, [M], V,
[LDV], [INFO])
CHARACTER(LEN=1) :: JOB, SIDE
INTEGER :: N, ILO, IHI, M, LDV, INFO
REAL(8), DIMENSION(:) :: LSCALE, RSCALE
REAL(8), DIMENSION(:,:) :: V
SUBROUTINE GGBAK_64(JOB, SIDE, [N], ILO, IHI, LSCALE, RSCALE, [M], V,
[LDV], [INFO])
CHARACTER(LEN=1) :: JOB, SIDE
INTEGER(8) :: N, ILO, IHI, M, LDV, INFO
REAL(8), DIMENSION(:) :: LSCALE, RSCALE
REAL(8), DIMENSION(:,:) :: V
C INTERFACE
#include <sunperf.h>
void dggbak(char job, char side, int n, int ilo, int ihi, double
*lscale, double *rscale, int m, double *v, int ldv, int
*info);
void dggbak_64(char job, char side, long n, long ilo, long ihi, double
*lscale, double *rscale, long m, double *v, long ldv, long
*info);
PURPOSEdggbak forms the right or left eigenvectors of a real generalized ei‐
genvalue problem A*x = lambda*B*x, by backward transformation on the
computed eigenvectors of the balanced pair of matrices output by DGG‐
BAL.
ARGUMENTS
JOB (input)
Specifies the type of backward transformation required:
= 'N': do nothing, return immediately;
= 'P': do backward transformation for permutation only;
= 'S': do backward transformation for scaling only;
= 'B': do backward transformations for both permutation and
scaling. JOB must be the same as the argument JOB supplied
to DGGBAL.
SIDE (input)
= 'R': V contains right eigenvectors;
= 'L': V contains left eigenvectors.
N (input) The number of rows of the matrix V. N >= 0.
ILO (input)
The integers ILO and IHI determined by DGGBAL. 1 <= ILO <=
IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
IHI (input)
See the description for ILO.
LSCALE (input)
Details of the permutations and/or scaling factors applied to
the left side of A and B, as returned by DGGBAL.
RSCALE (input)
Details of the permutations and/or scaling factors applied to
the right side of A and B, as returned by DGGBAL.
M (input) The number of columns of the matrix V. M >= 0.
V (input/output)
On entry, the matrix of right or left eigenvectors to be
transformed, as returned by DTGEVC. On exit, V is overwrit‐
ten by the transformed eigenvectors.
LDV (input)
The leading dimension of the matrix V. LDV >= max(1,N).
INFO (output)
= 0: successful exit.
< 0: if INFO = -i, the i-th argument had an illegal value.
FURTHER DETAILS
See R.C. Ward, Balancing the generalized eigenvalue problem,
SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.
6 Mar 2009 dggbak(3P)
