subroutine cggbak (JOB, SIDE, N, ILO, IHI, LSCALE, RSCALE, M, V, LDV, INFO)
CGGBAK
CGGBAK
Purpose:
CGGBAK forms the right or left eigenvectors of a complex generalized eigenvalue problem A*x = lambda*B*x, by backward transformation on the computed eigenvectors of the balanced pair of matrices output by CGGBAL.
Parameters:
JOB is CHARACTER*1
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 CGGBAL.
SIDE
SIDE is CHARACTER*1
= 'R': V contains right eigenvectors;
= 'L': V contains left eigenvectors.
N
N is INTEGER
The number of rows of the matrix V. N >= 0.
ILO
ILO is INTEGER
IHI
IHI is INTEGER
The integers ILO and IHI determined by CGGBAL.
1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.
LSCALE
LSCALE is REAL array, dimension (N)
Details of the permutations and/or scaling factors applied
to the left side of A and B, as returned by CGGBAL.
RSCALE
RSCALE is REAL array, dimension (N)
Details of the permutations and/or scaling factors applied
to the right side of A and B, as returned by CGGBAL.
M
M is INTEGER
The number of columns of the matrix V. M >= 0.
V
V is COMPLEX array, dimension (LDV,M)
On entry, the matrix of right or left eigenvectors to be
transformed, as returned by CTGEVC.
On exit, V is overwritten by the transformed eigenvectors.
LDV
LDV is INTEGER
The leading dimension of the matrix V. LDV >= max(1,N).
INFO
INFO is INTEGER
= 0: successful exit.
< 0: if INFO = -i, the i-th argument had an illegal value.
Author:
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date:
Further Details:
See R.C. Ward, Balancing the generalized eigenvalue problem,
SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.
Definition at line 150 of file cggbak.f.
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