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Re: new snapshot?


From: Søren Hauberg
Subject: Re: new snapshot?
Date: Thu, 25 Feb 2010 13:40:41 -0800

tor, 25 02 2010 kl. 16:25 -0500, skrev John W. Eaton:
> That fixed all the eigs failures for me, but I'm still seeing the
> following failure in svds, which uses eigs:
> 
>   >>>>> processing /export/home/jwe/src/octave/scripts/sparse/svds.m
>     ***** testif HAVE_ARPACK
>    [u2,s2,v2,flag] = svds(a,k,0);
>    s2 = diag(s2);
>    assert(flag,!1);
>    assert(s(k:-1:1), s2, 1e-10); 
>   !!!!! test failed
>   assert (s (k:-1:1),s2,1e-10) expected
>      38.060
>      38.060
>      38.034
>      38.034
>      38.015
>      38.015
>      38.004
>   but got
>      38.060
>      38.034
>      38.034
>      38.015
>      38.015
>      38.004
>      38.004
>   maximum absolute error 0.0263523 exceeds tolerance 1e-10
> 
> The test is:
> 
>   n = 100;
>   k = 7;
>   a = 
> sparse([3:n,1:n,1:(n-2)],[1:(n-2),1:n,3:n],[ones(1,n-2),0.4*n*ones(1,n),ones(1,n-2)]);
>   [u,s,v] = svd(full(a));
>   s = diag(s);
>   [dum, idx] = sort(abs(s));
>   s = s(idx);
>   u = u(:,idx);
>   v = v(:,idx);
>   randn('state',42)
> 
>   [u2,s2,v2,flag] = svds(a,k,0);
>   s2 = diag(s2);
>   assert(flag,!1);
>   assert(s(k:-1:1), s2, 1e-10); 
> 
> If I run this test in a copy of Octave compiled *without* --enable-64,
> I sometimes see also the error now.  The problem does not happen every
> time I run the test.  So it seems like some kind of memory error, but
> valgrind is not telling me anything.
> 
> I'm compiling with CXXFLAGS=-ggdb3 CFLAGS=-ggdb3, GCC version 4.4.3
> 20100108 (prerelease) (Debian 4.4.2-9) on an amd64 system.
> 
> Can anyone else duplicate this problem?

I am seeing this problem on a checkout from before your changes (haven't
tried with your changes):
        
        $ hg tip
        changeset:   10339:de2d43bcb083
        tag:         tip
        user:        Jaroslav Hajek <address@hidden>
        date:        Fri Feb 19 11:47:47 2010 +0100
        summary:     optimize some lazy index operations

This is on an AMD64 system running a 32-bit Ubuntu install. Perhaps this
is related to running a 32-bit OS on a 64-bit machine?

I got CXXFLAGS='-g -O2' using gcc 4.4.1.

Soren



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