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From Dimitri Pourbaix <pourb...@astro.ulb.ac.be>
Subject Re: [math] Status of MATH-327?
Date Wed, 17 Mar 2010 11:23:09 GMT
Hi,

>> 28: there is still one spurious non zero singular value
>> (3.547702387229884E-7 which I am going to try to kick out) instead of
>> two.
>>
>> Dim.
>
> I pushed it to 2.2 because what remained to resolve did not look to
> me like a showstopper for 2.1.  I may be missing something, though,
> regarding severity.  I am fine getting this into 2.1 if you have a fix.

I just checked the code and notice the problem is already present at the
exit of TriDiagonalTransform.  In order to compute SVD, one computes the
eigen decomposition of A^tA which relies upon the Householder tri-diagonal
transformation.  The tri-diagonal maxtrix still has 3 non-zero main diagonal
elements.  The smallest one is about 1.e-13, i.e. slightly too large to be
considered null against the largest, about 900.0

Right now, I see no option but avoiding the computation of A^tA.  It is
fair to ask for 2.2.

Regards,
  Dim.
----------------------------------------------------------------------------
Dimitri Pourbaix                         *
Institut d'Astronomie et d'Astrophysique *      Don't worry, be happy
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Universite Libre de Bruxelles            *
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  B-1050 Bruxelles                        *      Fax : +32-2-650.42.26
http://sb9.astro.ulb.ac.be/~pourbaix     * mailto:pourbaix@astro.ulb.ac.be

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