CGGBAK
November 2006
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.
eigenvalue problem A*x = lambda*B*x, by backward transformation on
the computed eigenvectors of the balanced pair of matrices output by
CGGBAL.
Arguments
| JOB |
(input) 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 |
(input) CHARACTER*1
= 'R': V contains right eigenvectors;
= 'L': V contains left eigenvectors. |
| N |
(input) INTEGER
The number of rows of the matrix V. N >= 0.
|
| ILO |
(input) INTEGER
|
| IHI |
(input) 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 |
(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 CGGBAL. |
| 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 CGGBAL. |
| M |
(input) INTEGER
The number of columns of the matrix V. M >= 0.
|
| V |
(input/output) 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 |
(input) INTEGER
The leading dimension of the matrix V. LDV >= max(1,N).
|
| INFO |
(output) INTEGER
= 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.
SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.