NAME

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( ∗ )

#include <sunperf.h>

void sgecon(char norm, int n, float ∗sa, int lda, float anorm, float ∗srcond, int ∗info) ;

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 matrix A, computed as RCOND = 1/(norm(A) ∗ 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 illegal value

SunOS 5.0  —  Last change: 10 Dec 1998