ZHECON(l) LAPACK routine (version 1.1) ZHECON(l)
NAME
ZHECON - estimate the reciprocal of the condition number of a complex Her-
mitian matrix A using the factorization A = U*D*U**H or A = L*D*L**H com-
puted by ZHETRF
SYNOPSIS
SUBROUTINE ZHECON( UPLO, N, A, LDA, IPIV, ANORM, RCOND, WORK, INFO )
CHARACTER UPLO
INTEGER INFO, LDA, N
DOUBLE PRECISION ANORM, RCOND
INTEGER IPIV( * )
COMPLEX*16 A( LDA, * ), WORK( * )
PURPOSE
ZHECON estimates the reciprocal of the condition number of a complex Hermi-
tian matrix A using the factorization A = U*D*U**H or A = L*D*L**H computed
by ZHETRF.
An estimate is obtained for norm(inv(A)), and the reciprocal of the condi-
tion 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.
A (input) COMPLEX*16 array, dimension (LDA,N)
The block diagonal matrix D and the multipliers used to obtain the
factor U or L as computed by ZHETRF.
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 structure of D as deter-
mined by ZHETRF.
ANORM (input) DOUBLE PRECISION
The 1-norm of the original matrix A.
RCOND (output) DOUBLE PRECISION
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) computed in this routine.
WORK (workspace) COMPLEX*16 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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