DSPTRI(3)
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
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 multipliers
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 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 DSPTRF.
 WORK (workspace) DOUBLE PRECISION 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.