DragonFly On-Line Manual Pages

PDGBTRF(l)                             )                            PDGBTRF(l)

NAME
       PDGBTRF - compute a LU factorization of an N-by-N real banded
       distributed matrix with bandwidth BWL, BWU

SYNOPSIS
       SUBROUTINE PDGBTRF( N, BWL, BWU, A, JA, DESCA, IPIV, AF, LAF, WORK,
                           LWORK, INFO )
           INTEGER BWL, BWU, INFO, JA, LAF, LWORK, N
           INTEGER DESCA( * ), IPIV( * )
           DOUBLE PRECISION A( * ), AF( * ), WORK( * )

PURPOSE
       PDGBTRF computes a LU factorization of an N-by-N real 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 PDGBTRS 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.

ScaLAPACK version 1.7           13 August 2001                      PDGBTRF(l)