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



NAME
       DPPTRI

SYNOPSIS
       SUBROUTINE DPPTRI (UPLO, N, AP, INFO)



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

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

           AP        (input/output)
                     AP is 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)
                     INFO is 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.



LAPACK routine                  31 October 2017                      DPPTRI(3)