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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.