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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] ordering of eigenvalues of EigenSolver
- From: Susanne Suter <susanne.suter@xxxxxxxxx>
- Date: Tue, 22 Feb 2011 08:57:16 +0100
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hi
thank you for taking the time to check that issue.
I noticed now that I use instead of EIG/SSYEV the function EIGS in
MatLab and the function SSYEVX in Lapack, which both return the x most
significant eigenvalues. so I've learned by now that there are two (or
more) types of eigenvalue decomposition methods provided in Matlab and
Lapack while eigen supports one.
thx again,
susanne
On Tue, Feb 22, 2011 at 8:35 AM, Gael Guennebaud
<gael.guennebaud@xxxxxxxxx> wrote:
> On Tue, Feb 22, 2011 at 1:18 AM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>>>
>>> Furthermore, other eigenvalue decomposition libraries seem to order
>>> eigenvalues, too. E.g., MatLab (based on ARPACK)
>>
>> Ah, I didn't know about Matlab.
>
> actually MatLab does as us and Lapack do, for instance:
>
> $ eig( diag([1 -1 2 -3 4]))'
>
> ans =
>
> -3 -1 1 2 4
>
> Same for Octave or Scilab.
>
> I don't see any reason to change for a convention that nobody follow
> while our current behavior seems to be quite standard.
>
> On the other hand we could allow for sorting capability such that user
> can easily sort rows or column as they like.
>
> gael
>
>
>