SSYTRI2(3)     LAPACK routine of NEC Numeric Library Collection     SSYTRI2(3)



NAME
       SSYTRI2

SYNOPSIS
       SUBROUTINE SSYTRI2 (UPLO, N, A, LDA, IPIV, WORK, LWORK, INFO)



PURPOSE
            SSYTRI2 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. SSYTRI2 sets the LEADING DIMENSION of the workspace
            before calling SSYTRI2X that actually computes the inverse.




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 NB 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 NB structure of D
                     as determined by SSYTRF.

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

           LWORK     (input)
                     LWORK is INTEGER
                     The dimension of the array WORK.
                     WORK is size >= (N+NB+1)*(NB+3)
                     If LDWORK = -1, then a workspace query is assumed; the routine
                      calculates:
                         - the optimal size of the WORK array, returns
                     this value as the first entry of the WORK array,
                         - and no error message related to LDWORK is issued by XERBLA.

           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                     SSYTRI2(3)