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From: "Tim Davis" <davis@cise.ufl.edu>
Newsgroups: comp.soft-sys.matlab
Subject: Re: multithreading with chol
Date: Tue, 7 Jul 2009 03:35:03 +0000 (UTC)
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"fabio freschi" <fabio.freschi@remove.gmail.com> wrote in message <h21thh$nro$1@fred.mathworks.com>...
> The exact call of chol I used is (of course)
> [L,p] = chol(A(ip,ip),'lower')
> sorry for the mistyping
> fabio

UMFPACK and CHOLMOD use the BLAS, and those benefit
from multithreading.  When Cleve Moler wrote that
"Cleve's Corner" article, there was a performance
bug in the BLAS that slowed it down when multithreading
was enabled.  That's no longer the case.  In a later
version of MATLAB (including 7.5) the bug was fixed.

Neither UMFPACK nor CHOLMOD include any explicit
parallelism.  They just call the BLAS (dense matrix
operations) which benefit from multithreading.

MATLAB uses the MKL BLAS, so UMFPACK and CHOLMOD should
get the same parallel speedup inside or outside of
MATLAB.

My sparse QR (SuiteSparseQR) does include explicit
multithreading (as well as calling the parallel BLAS),
but it's not used in the sparse QR in MATLAB.