dsptri(3)

NAME

DSPTRI - compute the inverse of a real symmetric indefi

nite matrix A in packed storage using the factorization A =

U*D*U**T or A = L*D*L**T computed by DSPTRF

SYNOPSIS

SUBROUTINE DSPTRI( UPLO, N, AP, IPIV, WORK, INFO )
    CHARACTER      UPLO
    INTEGER        INFO, N
    INTEGER        IPIV( * )
    DOUBLE         PRECISION AP( * ), WORK( * )

PURPOSE

DSPTRI computes the inverse of a real symmetric indefinite

matrix A in packed storage using the factorization A = U*D*U**T

or A = L*D*L**T computed by DSPTRF.

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.

AP (input/output) DOUBLE PRECISION array, dimension

(N*(N+1)/2)

On entry, the block diagonal matrix D and the mul

tipliers used to obtain the factor U or L as computed by DSPTRF,

stored as a packed triangular matrix.

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

the original matrix, stored as a packed triangular matrix. The j

th column of inv(A) is stored in the array AP as follows: if UPLO

= 'U', AP(i + (j-1)*j/2) = inv(A)(i,j) for 1<=i<=j; if UPLO =

'L', AP(i + (j-1)*(2n-j)/2) = inv(A)(i,j) for j<=i<=n.

IPIV (input) INTEGER array, dimension (N)

Details of the interchanges and the block struc

ture of D as determined by DSPTRF.

WORK (workspace) DOUBLE PRECISION array, dimension (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

DSPTRI(3)