SSYTRI2X(3)    LAPACK routine of NEC Numeric Library Collection    SSYTRI2X(3)



NAME
       SSYTRI2X

SYNOPSIS
       SUBROUTINE SSYTRI2X (UPLO, N, A, LDA, IPIV, WORK, NB, INFO)



PURPOSE
            SSYTRI2X 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
            SSYTRF.




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.

           A         (input/output)
                     A is REAL array, dimension (LDA,N)
                     On entry, the NNB diagonal matrix D and the multipliers
                     used to obtain the factor U or L as computed by SSYTRF.

                     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)
                     LDA is INTEGER
                     The leading dimension of the array A.  LDA >= max(1,N).

           IPIV      (input)
                     IPIV is INTEGER array, dimension (N)
                     Details of the interchanges and the NNB structure of D
                     as determined by SSYTRF.

           WORK      (output)
                     WORK is REAL array, dimension (N+NNB+1,NNB+3)

           NB        (input)
                     NB is INTEGER
                     Block size

           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                    SSYTRI2X(3)