[SciPy-dev] ARPACK wrapper

Aric Hagberg hagberg at lanl.gov
Mon Nov 20 08:33:26 CST 2006


On Mon, Nov 20, 2006 at 09:45:47AM +0100, Nils Wagner wrote:
> Hi Neilen,
> 
> In order to compare the results with the workhorse eig I have used a
> very small
> order n. The number of desired eigenpairs is equal to k=4 in my example,
> but the
> shape of the array of eigenvectors is (n,k+1) and for the eigenvalues it
> is (k+1,).
> The eigenvectors returned by arpack.eigen are zero.
> 
> Nils

Hi Nils,

The size of the return arrays are intentional (k+1).  This is 
the way ARPACK returns eigenvalues and eigenvectors for nonsymmetric
matrices.  I think the idea is that the k'th eigenvalue
(largest, smallest, etc) might be a complex conjugate pair and
then you might want k+1 (the conjugate).  Else, if the k'th
eigenvalue is real that entry is zero.   

I can run your test example successfully.  Do the tests in
arpack/tests/test_arpack.py work for you?  

Aric

 



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