PDDTTRF - compute a LU factorization of an N-by-N real tridiagonal diagonally dominant-like distributed

       PDDTTRF  -  compute a LU factorization of an N-by-N real tridiagonal diagonally dominant-like distributed
       matrix A(1:N, JA:JA+N-1)

       PDDTTRF computes a LU factorization of an N-by-N real tridiagonal  diagonally  dominant-like  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 PDDTTRS to solve linear systems.

       The factorization has the form

               P A(1:N, JA:JA+N-1) P^T = L U

       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                                        PDDTTRF(l)

       SUBROUTINE PDDTTRF( N, DL, D, DU, JA, DESCA, AF, LAF, WORK, LWORK, INFO )

           INTEGER         INFO, JA, LAF, LWORK, N

           INTEGER         DESCA( * )

           DOUBLE          PRECISION AF( * ), D( * ), DL( * ), DU( * ), WORK( * )