Gentoo Archives: gentoo-science

From: Andrea Arteaga <andyspiros@×××××.com>
To: gentoo-science@l.g.o
Subject: Re: [gentoo-science] Atlas giving wrong results on matrix multiplication
Date: Mon, 19 Sep 2011 15:17:38
In Reply to: [gentoo-science] Atlas giving wrong results on matrix multiplication by "Xavier Fernández i Marín"
Dear Xavier,

thank you for your email and sorry for the late reply.
In theory it should be useless to provide optimization flags when
compiling ATLAS, because it automatically uses and tests many flags,
but I could be wrong.

How did you install ATLAS? From the science overlay? I suggest that
you update it. Now in the overlay we have sci-libs/atlas-3.9.49
(~keyworded) [BTW, I will probably bump the version to 3.9.51 today].
Could you install it and redo the test? Otherwise, could you shortly
explain how to reproduce the problem, so that I can try?

Andrea Arteaga

2011/9/14 Xavier Fernández i Marín <xfim.ll@×××××.com>:
> Dear all, > > I recently submitted a question to the R-help mailing list, because I > noticed that matrix multiplication was giving me trouble (basically, that > there were some times when a result was NaN): > > > > As it is mentioned in the end of the thread, the solution was to recompile > R against the reference blas and lapack libraries, and avoid the atlas > that I was using. > > So it seems that the problem is not R-related, but atlas-related, and > linked to gentoo, I would like to share the problem with you, just in case > somebody has any clue on what is wrong with atlas. > > Although I have firstly used a very aggressive cflags to compile atlas > (-Ofast), I suspected that the problem was that, but I recompiled atlas > using -O2 and the problem still presists with atlas, but is solved with > reference. > > I am using atlas-3.9.23-r4, R-2.13.1 and gcc-4.6.1.


Subject Author
Re: [gentoo-science] Atlas giving wrong results on matrix multiplication "Xavier Fernández i Marín" <xfim.ll@×××××.com>