[Octave-bug-tracker] [bug #49523] eigs (R2013b and later) uses NaNs, not zeros, for unconverged Ritz values

[Rik]

Follow-up Comment #12, bug #49523 (project octave):

The unconverged Ritz values represent an exceptional case.  It is important to
warn about them, but the exact form of the warning is not that critical.  My
suggestion was to set only the real portion to NaN.  After that, I would rely
on Octave's automatic narrowing to change a complex matrix, with all imaginary
parts equal to zero, to a real matrix.  If the matrix can't be narrowed
because there are non-zero complex values then you do get


NaN + 0.00000i


but that is okay for me since the NaN stands out as the first thing in the
entry, and isnan returns true if either the real or imaginary part is NaN.



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