.TH PDPTTRF l "12 May 1997" "LAPACK version 1.5" "LAPACK routine (version 1.5)"
.SH NAME
PDPTTRF \- compute a Cholesky factorization of an N-by-N real tridiagonal symmetric positive definite distributed matrix A(1:N, JA:JA+N-1)
.SH SYNOPSIS
.TP 20
SUBROUTINE PDPTTRF(
N, D, E, JA, DESCA, AF, LAF, WORK, LWORK,
INFO )
.TP 20
.ti +4
INTEGER
INFO, JA, LAF, LWORK, N
.TP 20
.ti +4
INTEGER
DESCA( * )
.TP 20
.ti +4
DOUBLE
PRECISION AF( * ), D( * ), E( * ), WORK( * )
.SH PURPOSE
PDPTTRF computes a Cholesky factorization
of an N-by-N real tridiagonal
symmetric positive definite distributed matrix
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
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subsequent calls to PDPTTRS to solve linear systems.
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The factorization has the form
.br

        P A(1:N, JA:JA+N-1) P^T = U' D U  or
.br

        P A(1:N, JA:JA+N-1) P^T = L D L',
.br

where U is a tridiagonal upper triangular matrix and L is tridiagonal
lower triangular, and P is a permutation matrix.
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