## SYNOPSIS

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

- INTEGER INFO, JA, LAF, LWORK, N

- INTEGER DESCA( * )

- REAL AF( * ), D( * ), DL( * ), DU( * ), WORK( * )

## PURPOSE

PSDTTRF 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 insubsequent calls to PSDTTRS 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.