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

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

       PSPTTRF 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 PSPTTRS 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                                        PSPTTRF(l)

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

           INTEGER         INFO, JA, LAF, LWORK, N

           INTEGER         DESCA( * )

           REAL            AF( * ), D( * ), E( * ), WORK( * )