PDPTTRF - compute a Cholesky factorization of an N-by-N real tridiagonal symmetric positive definite

       PDPTTRF  -  compute  a  Cholesky  factorization of an N-by-N real tridiagonal symmetric positive definite
       distributed matrix A(1:N, JA:JA+N-1)

       PDPTTRF computes a Cholesky factorization of an  N-by-N  real  tridiagonal  symmetric  positive  definite
       distributed  matrix  A(1:N, JA:JA+N-1).  Reordering is used to increase parallelism in the factorization.
       This reordering results in factors that are DIFFERENT from those produced by equivalent sequential codes.
       These factors cannot be used directly by users; however, they can be used in
       subsequent calls to PDPTTRS to solve linear systems.

       The factorization has the form

               P A(1:N, JA:JA+N-1) P^T = U' D U  or

               P A(1:N, JA:JA+N-1) P^T = L D L',

       where U is a tridiagonal upper triangular matrix and L is  tridiagonal  lower  triangular,  and  P  is  a
       permutation matrix.

LAPACK version 1.5                                 12 May 1997                                        PDPTTRF(l)

       SUBROUTINE PDPTTRF( N, D, E, JA, DESCA, AF, LAF, WORK, LWORK, INFO )

           INTEGER         INFO, JA, LAF, LWORK, N

           INTEGER         DESCA( * )

           DOUBLE          PRECISION AF( * ), D( * ), E( * ), WORK( * )