
DGECON(l) ) DGECON(l)
NAME
DGECON  estimate the reciprocal of the condition number of a general real matrix A, in
either the 1norm or the infinitynorm, 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( * )
PURPOSE
DGECON estimates the reciprocal of the condition number of a general real matrix A, in
either the 1norm or the infinitynorm, using the LU factorization computed by DGETRF. An
estimate is obtained for norm(inv(A)), and the reciprocal of the condition number is com
puted as
RCOND = 1 / ( norm(A) * norm(inv(A)) ).
ARGUMENTS
NORM (input) CHARACTER*1
Specifies whether the 1norm condition number or the infinitynorm condition num
ber is required:
= '1' or 'O': 1norm;
= 'I': Infinitynorm.
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 1norm of the original matrix A. If NORM = 'I', the
infinitynorm 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 ith argument had an illegal value
LAPACK version 3.0 15 June 2000 DGECON(l) 
