Section: LAPACK routine (version 1.5) (l)Updated: 12 May 1997Local indexUp

NAME

PCGBTRF - compute a LU factorization of an N-by-N complex banded distributed matrix with bandwidth BWL, BWU

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 in
subsequent 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.