[eigen] Partial eigenvalue decomposition

[Romain Brégier <r.bregier@xxxxxxxxxxx>]

Hi,

Is there a way with Eigen to retrieve only the k first eigenvalues and 
eigenvectors of a nxn self adjoint positive matrix (considering the 
eigenvalues in decreasing order, and k < n)?
I did not find such a tool in the documentation but maybe I missed 
something.

Thanks,
Romain