[SciPy-dev] Comments on API for Matlab's eigs equivalent (computing a few eigenvalues only)

Anne Archibald peridot.faceted@gmail....
Thu Feb 4 14:18:02 CST 2010

On 4 February 2010 15:01, Rob Clewley <rob.clewley@gmail.com> wrote:
> On Thu, Feb 4, 2010 at 2:31 PM, David Warde-Farley <dwf@cs.toronto.edu> wrote:
>> On 4-Feb-10, at 3:12 AM, Dag Sverre Seljebotn wrote:
>>
>>> I feel there's also a certain convention of listing the largest
>>> eigenvalues first; "let \lambda_i be the eigenvalues...assume
>>> \lambda_2
>>> < \lambda_1 ...".
>>
>> +1, though I've seen them listed from smallest to largest as well.
>>
>> David
>
> I'm +1 too, but are these going to be ordered by norm of the
> eigenvalue if they are complex, or by the real part only? I suggest by
> norm, and the docstring needs to make the choice clear. This
> functionality has to be consistent for all uses of eig()!

I have to say using the norm for complex eigenvalues is asking for
trouble, since it puts -2 between 1 and 3. Not that this is relevant
for a symmetric (Hermitian) eigensolver, which will always have real
eigenvalues.

Anne