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# chpcon

```
NAME
CHPCON - estimate the reciprocal of the condition number of
a complex Hermitian packed matrix A using the factorization
A = U*D*U**H or A = L*D*L**H computed by CHPTRF

SYNOPSIS
SUBROUTINE CHPCON( UPLO, N, AP, IPIV, ANORM, RCOND, WORK,
INFO )

CHARACTER      UPLO

INTEGER        INFO, N

REAL           ANORM, RCOND

INTEGER        IPIV( * )

COMPLEX        AP( * ), WORK( * )

PURPOSE
CHPCON estimates the reciprocal of the condition number of a
complex Hermitian packed matrix A using the factorization A
= U*D*U**H or A = L*D*L**H computed by CHPTRF.

An estimate is obtained for norm(inv(A)), and the reciprocal
of the condition number is computed as RCOND = 1 / (ANORM *
norm(inv(A))).

ARGUMENTS
UPLO    (input) CHARACTER*1
Specifies whether the details of the factorization
are stored as an upper or lower triangular matrix.
= 'U':  Upper triangular, form is A = U*D*U**H;
= 'L':  Lower triangular, form is A = L*D*L**H.

N       (input) INTEGER
The order of the matrix A.  N >= 0.

AP      (input) COMPLEX array, dimension (N*(N+1)/2)
The block diagonal matrix D and the multipliers used
to obtain the factor U or L as computed by CHPTRF,
stored as a packed triangular matrix.

IPIV    (input) INTEGER array, dimension (N)
Details of the interchanges and the block structure
of D as determined by CHPTRF.

ANORM   (input) REAL
The 1-norm of the original matrix A.

RCOND   (output) REAL

The reciprocal of the condition number of the matrix
A, computed as RCOND = 1/(ANORM * AINVNM), where
AINVNM is an estimate of the 1-norm of inv(A) com-
puted in this routine.

WORK    (workspace) COMPLEX array, dimension (2*N)

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