sgebak(3)

NAME

SGEBAK - form the right or left eigenvectors of a real

general matrix by backward transformation on the computed eigen

vectors of the balanced matrix output by SGEBAL

SYNOPSIS

SUBROUTINE SGEBAK( JOB, SIDE, N, ILO, IHI,  SCALE,  M,  V,
LDV, INFO )
    CHARACTER      JOB, SIDE
    INTEGER        IHI, ILO, INFO, LDV, M, N
    REAL           V( LDV, * ), SCALE( * )

PURPOSE

SGEBAK forms the right or left eigenvectors of a real gen

eral matrix by backward transformation on the computed eigenvec

tors of the balanced matrix output by SGEBAL.

ARGUMENTS

JOB (input) CHARACTER*1

Specifies the type of backward transformation re

quired: = 'N', do nothing, return immediately; = 'P', do backward

transformation for permutation only; = 'S', do backward transfor

mation for scaling only; = 'B', do backward transformations for

both permutation and scaling. JOB must be the same as the argu

ment JOB supplied to SGEBAL.

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

IHI=0, if N=0.

SCALE (input) REAL array, dimension (N)

Details of the permutation and scaling factors, as

returned by SGEBAL.

M (input) INTEGER

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

V (input/output) REAL array, dimension (LDV,M)

On entry, the matrix of right or left eigenvectors

to be transformed, as returned by SHSEIN or STREVC. On exit, V

is overwritten by the transformed eigenvectors.

LDV (input) INTEGER

The leading dimension of the array V. LDV >=

max(1,N).

INFO (output) INTEGER

= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille

gal value.

LAPACK version 3.0 15 June 2000

SGEBAK(3)