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# cgecon

```
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 )

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
```