[Octave-bug-tracker] [bug #41305] eigs: error -14 in dneupd when requesting fewer eigenvalues

[Marco Caliari]

Follow-up Comment #20, bug #41305 (project octave):

I checked with 4.2.0 the sweepseed test in comment #17 and I confirm the
results (about 2% failures with both Octave and Matlab). I also think this is
an issue in Arpack:

If possible, it is best to avoid setting nev (k in Octave) in a way that will
split clusters of eigenvalues. [ARPACK Users' Guide, p.16]

A workaround could be to set k at least to 6 (which is the default value) and
to return the desired number of eigenvalues. I worked on something similar in
#45153, it should be not that difficult to implement.

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