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

- 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( * )

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.