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- To: eigen@xxxxxxxxxxxxxxxxxxx
- Subject: Re: [eigen] ordering of eigenvalues of EigenSolver
- From: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>
- Date: Tue, 8 Feb 2011 11:51:09 -0500
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2011/2/8 Milian Wolff <mail@xxxxxxxxxx>:
> Susanne Suter, 08.02.2011:
>> Hi
>>
>> Sorry, I accidently hit the "send button" too early. Here my complete
>> messge again.
>>
>> I'm testing the Eigen library in order to use it for eigenvalue
>> decomposition or SVD. In the end I need the eigenvectors (left
>> singular vectors) and the eigenvalues (singular values).
>>
>> I noticed that when using the EigenSolver classes, the ordering of the
>> eigenvalues is not as I expected.
>
> as I was teached: the ordering of eigen values is totally arbitrary and
> depends on the implemented algorithm. Meaning: You have to sort them to your
> expectations.
For decompositions that produce real values, such as
SelfAdjointEigenSolver and SVD, we definitely want to order
eigenvalues in decreasing order. Not doing that would be a bug.
For decompositions that do not produce real values, such as
EigenSolver, there is no 'natural' order so there's nothing useful for
us to do.
Sorry, no time to check now what we are actually doing.
Benoit
>
> bye
> --
> Milian Wolff
> mail@xxxxxxxxxx
> http://milianw.de
>