DPPTRI (3lapack)

compute the inverse of a real symmetric positive definite matrix A using the Cholesky factorization A = U**T*U or A = L*L**T computed by DPPTRF

SYNOPSIS

  SUBROUTINE DPPTRI( UPLO, N, AP, INFO )

      CHARACTER      UPLO

      INTEGER        INFO, N

      DOUBLE         PRECISION AP( * )

PURPOSE

  DPPTRI computes the inverse of a real symmetric positive definite matrix A
  using the Cholesky factorization A = U**T*U or A = L*L**T computed by
  DPPTRF.

ARGUMENTS

  UPLO    (input) CHARACTER*1
          = 'U':  Upper triangular factor is stored in AP;
          = 'L':  Lower triangular factor is stored in AP.

  N       (input) INTEGER
          The order of the matrix A.  N >= 0.

  AP      (input/output) DOUBLE PRECISION array, dimension (N*(N+1)/2)
          On entry, the triangular factor U or L from the Cholesky
          factorization A = U**T*U or A = L*L**T, packed columnwise as a
          linear array.  The j-th column of U or L is stored in the array AP
          as follows: if UPLO = 'U', AP(i + (j-1)*j/2) = U(i,j) for 1<=i<=j;
          if UPLO = 'L', AP(i + (j-1)*(2n-j)/2) = L(i,j) for j<=i<=n.

          On exit, the upper or lower triangle of the (symmetric) inverse of
          A, overwriting the input factor U or L.

  INFO    (output) INTEGER
          = 0:  successful exit
          < 0:  if INFO = -i, the i-th argument had an illegal value
          > 0:  if INFO = i, the (i,i) element of the factor U or L is zero,
          and the inverse could not be computed.