Section: LAPACK routine (version 1.5) (l)Updated: 12 May 1997Local indexUp
PDGBTRF - compute a LU factorization of an N-by-N real banded distributed matrix with bandwidth BWL, BWU
N, BWL, BWU, A, JA, DESCA, IPIV, AF, LAF,
WORK, LWORK, INFO )
BWL, BWU, INFO, JA, LAF, LWORK, N
DESCA( * ), IPIV( * )
PRECISION A( * ), AF( * ), WORK( * )
PDGBTRF computes a LU factorization
of an N-by-N real banded
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.