# sgebak (l) - Linux Man Pages

## NAME

SGEBAK - forms the right or left eigenvectors of a real general matrix by backward transformation on the computed eigenvectors 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 general matrix by backward transformation on the computed eigenvectors of the balanced matrix output by SGEBAL.

## ARGUMENTS

JOB (input) CHARACTER*1
Specifies the type of backward transformation required: = aqNaq, do nothing, return immediately; = aqPaq, do backward transformation for permutation only; = aqSaq, do backward transformation for scaling only; = aqBaq, do backward transformations for both permutation and scaling. JOB must be the same as the argument JOB supplied to SGEBAL.
SIDE (input) CHARACTER*1
= aqRaq: V contains right eigenvectors;
= aqLaq: 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 illegal value.