PSGBTRF(3)    ScaLAPACK routine of NEC Numeric Library Collection   PSGBTRF(3)



NAME
       PSGBTRF  -  compute  a  LU  factorization of an N-by-N real banded dis-
       tributed matrix with bandwidth BWL, BWU

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

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

           INTEGER         DESCA( * ), IPIV( * )

           REAL            A( * ), AF( * ), WORK( * )

PURPOSE
       PSGBTRF  computes  a  LU  factorization  of  an N-by-N real banded dis-
       tributed 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; how-
       ever, they can be used in
       subsequent calls to PSGBTRS 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  tri-
       angular, 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 routine               31 October 2017                     PSGBTRF(3)