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From Luc Maisonobe <Luc.Maison...@free.fr>
Subject Re: [math] 2.1 Release plan
Date Sun, 14 Mar 2010 20:21:45 GMT
Dimitri Pourbaix a écrit :
> Luc,
> 
>> Concerning MATH-321, the partial fix I proposed has been withdrawn by
>> the complete rewrite of SVD.
>> This partial fix also was not considered mathematically sound by Dimitri
>> since the dimensions of the matrices did not match complete SVD. Well,
>> this was in fact desired as MATH-321 explicitly asks for non-full SVD.
>>
>> So I'm not sure anymore what we need to do. If we follow Dimitri's
>> rationale, we should close this as WON'T FIX. If we decide to fix it, I
>> think we should postpone it to after 2.1 to have time to decide how we
>> solve it. SVD has already been vastly improved by Dimitri's work, so I
>> would really much like to see it published now.
>>
>> Dim, what do you think about this ?
> 
> The version I uploaded does not benefit from any sparsity of the matrix
> to be decomposed.  I have not looked at any algorithm for this kind of
> matrix as it would likely involve a different way of storing the matrix
> itself.  I agree to put "WON'T FIX" for 321 unless someone can come up
> with an example showing that that, for a sparse matrix, the present
> version does not return the right answer.

I think there are two parts in the isse.
The first one is related to sparse matrix and we don't have an answer
yet. The second part is related to compute a partial set of singular
values. This is used for example in image compression or to find a
matrix with reduce rank that is the closest possible to an input matrix.
for this part, we may have an answer.

So for the first part, I think WON'T FIX may be an answer (or
INCOMPLETE, asking for a patch ...). For the second part, I would
suggest to simply postpone to 3.0.

Luc

> 
> 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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