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From Phil Steitz <phil.ste...@gmail.com>
Subject Re: [math] Status of MATH-327?
Date Wed, 17 Mar 2010 15:44:59 GMT
Dimitri Pourbaix wrote:
> 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.

OK, so you are OK with keeping the fix version for this one at 2.2?

Phil
> 
> Regards,
>  Dim.
> ----------------------------------------------------------------------------
> 
> Dimitri Pourbaix                         *
> Institut d'Astronomie et d'Astrophysique *      Don't worry, be happy
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> http://sb9.astro.ulb.ac.be/~pourbaix     * mailto:pourbaix@astro.ulb.ac.be
> 
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