# zgecon.f - Man Page

SRC/zgecon.f

## Synopsis

### Functions/Subroutines

subroutine zgecon (norm, n, a, lda, anorm, rcond, work, rwork, info)
ZGECON

## Function/Subroutine Documentation

### subroutine zgecon (character norm, integer n, complex*16, dimension( lda, * ) a, integer lda, double precision anorm, double precision rcond, complex*16, dimension( * ) work, double precision, dimension( * ) rwork, integer info)

ZGECON

Purpose:

``` ZGECON 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 ZGETRF.

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)) ).```
Parameters

NORM

```          NORM is 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

```          N is INTEGER
The order of the matrix A.  N >= 0.```

A

```          A is COMPLEX*16 array, dimension (LDA,N)
The factors L and U from the factorization A = P*L*U
as computed by ZGETRF.```

LDA

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

ANORM

```          ANORM is 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

```          RCOND is DOUBLE PRECISION
The reciprocal of the condition number of the matrix A,
computed as RCOND = 1/(norm(A) * norm(inv(A))).```

WORK

`          WORK is COMPLEX*16 array, dimension (2*N)`

RWORK

`          RWORK is DOUBLE PRECISION array, dimension (2*N)`

INFO

```          INFO is INTEGER
= 0:  successful exit
< 0:  if INFO = -i, the i-th argument had an illegal value.
NaNs are illegal values for ANORM, and they propagate to
the output parameter RCOND.
Infinity is illegal for ANORM, and it propagates to the output
parameter RCOND as 0.
= 1:  if RCOND = NaN, or
RCOND = Inf, or
the computed norm of the inverse of A is 0.
In the latter, RCOND = 0 is returned.```
Author

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line 130 of file zgecon.f.

## Author

Generated automatically by Doxygen for LAPACK from the source code.

## Referenced By

The man page zgecon(3) is an alias of zgecon.f(3).

Tue Nov 28 2023 12:08:42 Version 3.12.0 LAPACK