NAME

dsytri - compute the inverse of a real symmetric indefinite matrix A using the factorization A = U∗D∗U∗∗T or A = L∗D∗L∗∗T computed by DSYTRF

SYNOPSIS

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

void dsytri(char uplo, long int n, double ∗da, long int lda,
long int ∗ipivot, long int ∗info)

CHARACTER UPLO

INTEGER INFO, LDA, N

INTEGER IPIV( ∗ )

DOUBLE PRECISION A( LDA, ∗ ), WORK( ∗ )

PURPOSE

DSYTRI computes the inverse of a real symmetric indefinite matrix A using the factorization A = U∗D∗U∗∗T or A = L∗D∗L∗∗T computed by DSYTRF. 
 

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) DOUBLE PRECISION 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 DSYTRF.
 
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 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 DSYTRF.

WORK    (workspace) DOUBLE PRECISION 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.

Sun, Inc.  —  Last change: 20 Sep 1996