Gentoo Logo
Gentoo Spaceship




Note: Due to technical difficulties, the Archives are currently not up to date. GMANE provides an alternative service for most mailing lists.
c.f. bug 424647
List Archive: gentoo-science
Navigation:
Lists: gentoo-science: < Prev By Thread Next > < Prev By Date Next >
Headers:
To: gentoo-science@g.o
From: Xavier Fernández i Marín <xfim.ll@...>
Subject: Re: Atlas giving wrong results on matrix multiplication
Date: Tue, 20 Sep 2011 07:17:07 +0200
Andrea Arteaga vas escriure el dia dl, 19 set 2011:

> 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.

Yes, Atlas tries to find the best options. However, I was worried because
I had -Ofast in CFLAGS, and thought that maybe some GCC optimizations were
harming the binary.

> 
> 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?

No, I simply use the atlas provided in the official gentoo branch.

François sent an email pointing that there was a problem with 3.9-xx, and
suggesting going bach to 3.8. This is what I did and it is working fine,
without errors. So I assume that, effectively, it was something related
to the 3.9 branch, rather than compiling options.

A simplification of the code that was giving trouble is:

-----8<---------------
B <- c(0, 4.9039)
for (l in 10:100) {
  X <- cbind(1, matrix(rnorm(l, 0, 3), ncol=1))
  X <- ics
  for (i in 1:1000) {
    M <- X %*% B
    w <- which(is.nan(M))
    l <- length(w) 
    if (l!=0) {
      print(paste("Length", l, "error(s) on", X[w,2], sep=" "))
    }
  }
}
-----8<---------------

Thank you,
-- 
-  Xavier  -


References:
Atlas giving wrong results on matrix multiplication
-- Xavier Fernández i Marín
Re: Atlas giving wrong results on matrix multiplication
-- Andrea Arteaga
Navigation:
Lists: gentoo-science: < Prev By Thread Next > < Prev By Date Next >
Previous by thread:
Re: Atlas giving wrong results on matrix multiplication
Next by thread:
g-octave
Previous by date:
Re: scilab-4 removal from the tree
Next by date:
Installing SPSS in gentoo linux


Updated Jul 05, 2012

Summary: Archive of the gentoo-science mailing list.

Donate to support our development efforts.

Copyright 2001-2013 Gentoo Foundation, Inc. Questions, Comments? Contact us.