Re: svds test failures

[Marco atzeri]

On 8/7/2011 3:16 PM, Marco atzeri wrote:
> On 8/6/2011 10:06 PM, Rik wrote:
>
> > > Date: Sat, 06 Aug 2011 12:18:15 +0200
> > > From: Marco atzeri
>
> > --------------
> >
> > I would say that there is something different about your compiled version
> > of ARPACK. The tests specifically use an initialization vector so the
> > ARPACK code should always start in the same location in solution space
> > and
> > find the same eigenvalues. It works on UNIX systems anyways. Are you
> > running an octave version> 3.4.0 when ARPACK was incorporated into
> > Octave's build? Might you have a leftover ARPACK library on your system
> > from a previous version of Octave?
> >
> > Cheers,
> > Rik
>
> Hi Rik,
>
> it is a recent source
>
> $ hg tip
> changeset: 12930:7bd29d875af1
> tag: tip
> user: Rik <address@hidden>
> date: Fri Aug 05 20:36:10 2011 -0700
> summary: mode.m: Eliminate cellfun usage in assert tests
>
> and from the build log I see no evidence that the system arpack
> is used, just the octave one and very recent (28 Jul)
>
> Marco

I just found that it is a matter of the start point,
changing from

 randn('state',42);
 rand('state',42)

to

 randn('state',43);
 rand('state',43)

and I have

> [u2,s2,v2,flag] = svds(A,k,0,opts);
> s2 = diag(s2)
s2 =

   38.060
   38.034
   38.034
   38.015
   38.015
   38.004
   38.004

without changing sigma.

It seems that the test is very sensible to the "rand state" value,
looking values around 42 (35 to 50) I have

35, 37, 40, 41, 43, 45, 46, 49, 50
all tests are fine

36, 39 , 47
almost all tests are fine, just need

assert (s,ones (6, 1),2 * eps)
changed to
assert (s,ones (6, 1),3 * eps)  # or 4*

as "maximum absolute error 6.66134e-16 exceeds tolerance 4.44089e-16"

the other values (38, 42, 44, 48 ) fails the sigma=0 test or
I get

assert (flag,!1) expected
0
but got
 1

already at the first test.
Is it possible that rand/randn are not producing the same value
on all the system, eventually due to different rounding ?

Regards
Marco