SGECON - estimate the reciprocal of the condition number
of a general real matrix A, in either the 1-norm or the
infinity-norm, using the LU factorization computed by
SGETRF
SYNOPSIS
SUBROUTINE SGECON( NORM, N, A, LDA, ANORM, RCOND, WORK,
IWORK, INFO )
CHARACTER NORM
INTEGER INFO, LDA, N
REAL ANORM, RCOND
INTEGER IWORK( * )
REAL A( LDA, * ), WORK( * )
PURPOSE
SGECON estimates the reciprocal of the condition number of
a general real matrix A, in either the 1-norm or the
infinity-norm, using the LU factorization computed by
SGETRF. An estimate is obtained for norm(inv(A)), and the
reciprocal of the condition number is computed as
RCOND = 1 / ( norm(A) * norm(inv(A)) ).
ARGUMENTS
NORM (input) CHARACTER*1
Specifies whether the 1-norm condition number or
the infinity-norm condition number is required:
= '1' or 'O': 1-norm;
= 'I': Infinity-norm.
N (input) INTEGER
The order of the matrix A. N >= 0.
A (input) REAL array, dimension (LDA,N)
The factors L and U from the factorization A =
P*L*U as computed by SGETRF.
LDA (input) INTEGER
The leading dimension of the array A. LDA >=
max(1,N).
ANORM (input) REAL
If NORM = '1' or 'O', the 1-norm of the original
matrix A. If NORM = 'I', the infinity-norm of the
original matrix A.
RCOND (output) REAL
The reciprocal of the condition number of the
norm(inv(A))).
WORK (workspace) REAL array, dimension (4*N)
IWORK (workspace) INTEGER array, dimension (N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an ille
gal value
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