SSPTRI(3)      LAPACK routine of NEC Numeric Library Collection      SSPTRI(3)



NAME
       SSPTRI

SYNOPSIS
       SUBROUTINE SSPTRI (UPLO, N, AP, IPIV, WORK, INFO)



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)
                     UPLO is 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)
                     N is INTEGER
                     The order of the matrix A.  N >= 0.

           AP        (input/output)
                     AP is REAL 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 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 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)
                     IPIV is INTEGER array, dimension (N)
                     Details of the interchanges and the block structure of D
                     as determined by SSPTRF.

           WORK      (output)
                     WORK is REAL array, dimension (N)

           INFO      (output)
                     INFO is 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.



LAPACK routine                  31 October 2017                      SSPTRI(3)