## SYNOPSIS

- 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( * )

## PURPOSE

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 insubsequent 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.