# chetri (l) - Linux Manuals

## NAME

CHETRI - computes the inverse of a complex Hermitian indefinite matrix A using the factorization A = U*D*U**H or A = L*D*L**H computed by CHETRF

## SYNOPSIS

SUBROUTINE CHETRI(
UPLO, N, A, LDA, IPIV, WORK, INFO )

CHARACTER UPLO

INTEGER INFO, LDA, N

INTEGER IPIV( * )

COMPLEX A( LDA, * ), WORK( * )

## PURPOSE

CHETRI computes the inverse of a complex Hermitian indefinite matrix A using the factorization A = U*D*U**H or A = L*D*L**H computed by CHETRF.

## ARGUMENTS

UPLO (input) CHARACTER*1
Specifies whether the details of the factorization are stored as an upper or lower triangular matrix. = aqUaq: Upper triangular, form is A = U*D*U**H;
= aqLaq: Lower triangular, form is A = L*D*L**H.
N (input) INTEGER
The order of the matrix A. N >= 0.
A (input/output) COMPLEX array, dimension (LDA,N)
On entry, the block diagonal matrix D and the multipliers used to obtain the factor U or L as computed by CHETRF. On exit, if INFO = 0, the (Hermitian) inverse of the original matrix. If UPLO = aqUaq, the upper triangular part of the inverse is formed and the part of A below the diagonal is not referenced; if UPLO = aqLaq the lower triangular part of the inverse is formed and the part of A above the diagonal is not referenced.
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 determined by CHETRF.
WORK (workspace) COMPLEX array, dimension (N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
> 0: if INFO = i, D(i,i) = 0; the matrix is singular and its inverse could not be computed.