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.

UPLO

          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

          N is INTEGER


          The order of the matrix A.  N >= 0.

A

          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

          LDA is INTEGER


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

IPIV

          IPIV is INTEGER array, dimension (N)


          Details of the interchanges and the NNB structure of D


          as determined by SSYTRF.

WORK

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

NB

          NB is INTEGER


          Block size

INFO

          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.

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

June 2017