
SSPTRI(l) ) SSPTRI(l)
NAME
SSPTRI  compute 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 SSPTRF
SYNOPSIS
SUBROUTINE SSPTRI( UPLO, N, AP, IPIV, WORK, INFO )
CHARACTER UPLO
INTEGER INFO, N
INTEGER IPIV( * )
REAL AP( * ), WORK( * )
PURPOSE
SSPTRI 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 SSPTRF.
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) REAL array, dimension (N*(N+1)/2)
On entry, the block diagonal matrix D and the multipliers used to obtain the fac
tor U or L as computed by SSPTRF, 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 jth column of inv(A) is stored in the array AP as
follows: if UPLO = 'U', AP(i + (j1)*j/2) = inv(A)(i,j) for 1<=i<=j; if UPLO =
'L', AP(i + (j1)*(2nj)/2) = inv(A)(i,j) for j<=i<=n.
IPIV (input) INTEGER array, dimension (N)
Details of the interchanges and the block structure of D as determined by SSPTRF.
WORK (workspace) REAL array, dimension (N)
INFO (output) INTEGER
= 0: successful exit
< 0: if INFO = i, the ith argument had an illegal value
> 0: if INFO = i, D(i,i) = 0; the matrix is singular and its inverse could not be
computed.
LAPACK version 3.0 15 June 2000 SSPTRI(l) 
