On 07/24/2011 09:10 PM, Jordi Gutiérrez Hermoso wrote:

> While porting Matlab code, I noticed that someone had used eigs for a

> 2x2 matrix, which produces an error to use eig instead. I patched the

> code to do that, but I inadverently introduced a bug because I forgot

> that eigs sorts its eigenvalues but eig does not.

>

> Should eigs be patched to call eig for small matrices and just sort

> them? Also, for the case of when you need all eigenvalues, should eigs

> just silently call eig instead of warning about it?

>

> - Jordi G. H.

>

The sorting rules aren't that obvious as the order of the values

returned might be largest eignevalue first, smallest first or even

sorted relative to a distance from a particular eigenvalue. So if matlab

does this it might be better to relax the error in eigs-base.cc to a

warning and letter ARPACK do the work.

David