[Octave-bug-tracker] [bug #53719] eigs delivers wron result in case of complex valued general eigenvalue problem

[Dan Sebald]

Follow-up Comment #1, bug #53719 (project octave):

Very timely bug report.  We're looking at similar issues here:

https://savannah.gnu.org/bugs/index.php?53700

(but that case is one which follows the "not sparse" path).

Just noting that these three cases work:

[Evectors Evalues] = eigs(A, B, 10, 'SM');
[Evectors Evalues] = eigs(A, B, 9, 'SM');
[Evectors Evalues] = eigs(A, B, 8, 'SM');

but going to

[Evectors Evalues] = eigs(A, B, 7, 'SM');

throws the eigenvalues out of alignment.  However, I think there is some
requirement in the __eigs__.cc and/or eigs-base.cc code that the NEV should
satisfy 2 <= NCV-NEV, so perhaps internally those first three above are
handled with a different algorithm--don't know.

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