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# dgecon

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( * )

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