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.TH SGGBAK l "15 June 2000" "LAPACK version 3.0" ")"
.SH NAME
SGGBAK - form the right or left eigenvectors of a real generalized eigenvalue problem A*x = lambda*B*x, by backward transformation on the computed eigenvectors of the balanced pair of matrices output by SGGBAL
.SH SYNOPSIS
.TP 19
SUBROUTINE SGGBAK(
JOB, SIDE, N, ILO, IHI, LSCALE, RSCALE, M, V,
LDV, INFO )
.TP 19
.ti +4
CHARACTER
JOB, SIDE
.TP 19
.ti +4
INTEGER
IHI, ILO, INFO, LDV, M, N
.TP 19
.ti +4
REAL
LSCALE( * ), RSCALE( * ), V( LDV, * )
.SH PURPOSE
SGGBAK forms the right or left eigenvectors of a real generalized eigenvalue problem A*x = lambda*B*x, by backward transformation on the computed eigenvectors of the balanced pair of matrices output by SGGBAL.
.SH ARGUMENTS
.TP 8
JOB (input) CHARACTER*1
Specifies the type of backward transformation required:
.br
= 'N': do nothing, return immediately;
.br
= 'P': do backward transformation for permutation only;
.br
= 'S': do backward transformation for scaling only;
.br
= 'B': do backward transformations for both permutation and
scaling.
JOB must be the same as the argument JOB supplied to SGGBAL.
.TP 8
SIDE (input) CHARACTER*1
= 'R': V contains right eigenvectors;
.br
= 'L': V contains left eigenvectors.
.TP 8
N (input) INTEGER
The number of rows of the matrix V. N >= 0.
.TP 8
ILO (input) INTEGER
IHI (input) INTEGER
The integers ILO and IHI determined by SGGBAL.
1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
.TP 8
LSCALE (input) REAL array, dimension (N)
Details of the permutations and/or scaling factors applied
to the left side of A and B, as returned by SGGBAL.
.TP 8
RSCALE (input) REAL array, dimension (N)
Details of the permutations and/or scaling factors applied
to the right side of A and B, as returned by SGGBAL.
.TP 8
M (input) INTEGER
The number of columns of the matrix V. M >= 0.
.TP 8
V (input/output) REAL array, dimension (LDV,M)
On entry, the matrix of right or left eigenvectors to be
transformed, as returned by STGEVC.
On exit, V is overwritten by the transformed eigenvectors.
.TP 8
LDV (input) INTEGER
The leading dimension of the matrix V. LDV >= max(1,N).
.TP 8
INFO (output) INTEGER
= 0: successful exit.
.br
< 0: if INFO = -i, the i-th argument had an illegal value.
.SH FURTHER DETAILS
See R.C. Ward, Balancing the generalized eigenvalue problem,
SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.
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