## SYNOPSIS

- SUBROUTINE PCGBTRF(
- N, BWL, BWU, A, JA, DESCA, IPIV, AF, LAF, WORK, LWORK, INFO )

- INTEGER BWL, BWU, INFO, JA, LAF, LWORK, N

- INTEGER DESCA( * ), IPIV( * )

- COMPLEX A( * ), AF( * ), WORK( * )

## PURPOSE

PCGBTRF computes a LU factorization of an N-by-N complex banded distributed matrix with bandwidth BWL, BWU: 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 PCGBTRS to solve linear systems.

The factorization has the form

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

where U is a banded upper triangular matrix and L is banded
lower triangular, and P and Q are permutation matrices.

The matrix Q represents reordering of columns

for parallelism's sake, while P represents

reordering of rows for numerical stability using

classic partial pivoting.