csytri(3)

NAME

CSYTRI - compute the inverse of a complex symmetric indef

inite matrix A using the factorization A = U*D*U**T or A =

L*D*L**T computed by CSYTRF

SYNOPSIS

SUBROUTINE CSYTRI( UPLO, N, A, LDA, IPIV, WORK, INFO )
    CHARACTER      UPLO
    INTEGER        INFO, LDA, N
    INTEGER        IPIV( * )
    COMPLEX        A( LDA, * ), WORK( * )

PURPOSE

CSYTRI computes the inverse of a complex symmetric indefi

nite matrix A using the factorization A = U*D*U**T or A =

L*D*L**T computed by CSYTRF.

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**T;
= 'L': Lower triangular, form is A = L*D*L**T.

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 mul

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

On exit, if INFO = 0, the (symmetric) inverse of

the original matrix. If UPLO = 'U', the upper triangular part of

the inverse is formed and the part of A below the diagonal is not

referenced; if UPLO = 'L' the lower triangular part of the in

verse is formed and the part of A above the diagonal is not ref

erenced.

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 CSYTRF.

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
> 0: if INFO = i, D(i,i) = 0; the matrix is singu

lar and its inverse could not be computed.

LAPACK version 3.0 15 June 2000

CSYTRI(3)