NAME

dgecon - 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 DGETRF

SYNOPSIS

SUBROUTINE DGECON( NORM, N, A, LDA, ANORM, RCOND, WORK, IWORK, INFO )

CHARACTER NORM

INTEGER INFO, LDA, N

DOUBLE PRECISION ANORM, RCOND

INTEGER IWORK( ∗ )

DOUBLE PRECISION A( LDA, ∗ ), WORK( ∗ )

#include <sunperf.h>

void dgecon(char norm, int n, double ∗da, int lda, double anorm, double ∗drcond, int ∗info) ;

PURPOSE

DGECON 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 DGETRF. 
 
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) DOUBLE PRECISION array, dimension (LDA,N)
The factors L and U from the factorization A = P∗L∗U as computed by DGETRF.

LDA (input) INTEGER
The leading dimension of the array A.  LDA >= max(1,N).

ANORM (input) DOUBLE PRECISION
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) DOUBLE PRECISION
The reciprocal of the condition number of the matrix A, computed as RCOND = 1/(norm(A) ∗ norm(inv(A))).

WORK (workspace) DOUBLE PRECISION 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