dggbak-f(3)

dggbak.f –

Synopsis

Functions/Subroutines

subroutine dggbak (JOB, SIDE, N, ILO, IHI, LSCALE, RSCALE, M, V, LDV, INFO)
DGGBAK

Function/Subroutine Documentation

subroutine dggbak (characterJOB, characterSIDE, integerN, integerILO, integerIHI, double precision, dimension( * )LSCALE, double precision, dimension( * )RSCALE, integerM, double precision, dimension( ldv, * )V, integerLDV, integerINFO)

DGGBAK

Purpose:

 DGGBAK 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
 DGGBAL.

Parameters:

JOB

 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 DGGBAL.

SIDE

 SIDE is CHARACTER*1
 = 'R': V contains right eigenvectors;
 = 'L': V contains left eigenvectors.

 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 DGGBAL.
 1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0.

LSCALE

 LSCALE is DOUBLE PRECISION array, dimension (N)
 Details of the permutations and/or scaling factors applied
 to the left side of A and B, as returned by DGGBAL.

RSCALE

 RSCALE is DOUBLE PRECISION array, dimension (N)
 Details of the permutations and/or scaling factors applied
 to the right side of A and B, as returned by DGGBAL.

 M is INTEGER
 The number of columns of the matrix V. M >= 0.

 V is DOUBLE PRECISION array, dimension (LDV,M)
 On entry, the matrix of right or left eigenvectors to be
 transformed, as returned by DTGEVC.
 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 Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Date:

November 2011

Further Details:

 See R.C. Ward, Balancing the generalized eigenvalue problem,
 SIAM J. Sci. Stat. Comp. 2 (1981), 141-152.

Definition at line 147 of file dggbak.f.

Author

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