NAME

cgecon - estimate the reciprocal of the condition number of a general complex matrix A, in either the 1-norm or the infinity-norm, using the LU factorization computed by CGETRF

SYNOPSIS

SUBROUTINE CGECON(
NORM, N, A, LDA, ANORM, RCOND, WORK, RWORK, INFO )

void cgecon(char norm, long int n, complex ∗ca, long int lda,
float anorm, float ∗srcond, long int ∗info)

CHARACTER NORM

INTEGER INFO, LDA, N

REAL ANORM, RCOND

REAL RWORK( ∗ )

COMPLEX A( LDA, ∗ ), WORK( ∗ )

PURPOSE

CGECON estimates the reciprocal of the condition number of a general complex matrix A, in either the 1-norm or the infinity-norm, using the LU factorization computed by CGETRF. 
 
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) COMPLEX array, dimension (LDA,N)
The factors L and U from the factorization A = P∗L∗U as computed by CGETRF.

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) COMPLEX array, dimension (2∗N)

RWORK   (workspace) REAL array, dimension (2∗N)

INFO    (output) INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value

Sun, Inc.  —  Last change: 20 Sep 1996