checon(3)

NAME

CHECON - estimate the reciprocal of the condition number

of a complex Hermitian matrix A using the factorization A =

U*D*U**H or A = L*D*L**H computed by CHETRF

SYNOPSIS

SUBROUTINE CHECON( UPLO, N, A, LDA,  IPIV,  ANORM,  RCOND,
WORK, INFO )
    CHARACTER      UPLO
    INTEGER        INFO, LDA, N
    REAL           ANORM, RCOND
    INTEGER        IPIV( * )
    COMPLEX        A( LDA, * ), WORK( * )

PURPOSE

CHECON estimates the reciprocal of the condition number of

a complex Hermitian matrix A using the factorization A = U*D*U**H

or A = L*D*L**H computed by CHETRF. An estimate is obtained for

norm(inv(A)), and the reciprocal of the condition number is com

puted 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.

A (input) COMPLEX array, dimension (LDA,N)

The block diagonal matrix D and the multipliers

used to obtain the factor U or L as computed by CHETRF.

LDA (input) INTEGER

The leading dimension of the array A. LDA >=

max(1,N).

IPIV (input) INTEGER array, dimension (N)

Details of the interchanges and the block struc

ture of D as determined by CHETRF.

ANORM (input) REAL

The 1-norm of the original matrix A.

RCOND (output) REAL

The reciprocal of the condition number of the ma

trix A, computed as RCOND = 1/(ANORM * AINVNM), where AINVNM is

an estimate of the 1-norm of inv(A) computed 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 ille

gal value

LAPACK version 3.0 15 June 2000

CHECON(3)