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dsptri

 NAME
      DSPTRI - compute 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.

 (N*(N+1)/2)
      AP      (input/output) DOUBLE PRECISION array, dimension
              On entry, the block diagonal matrix D and the multi-
              pliers 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 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) 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 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.