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

[Rik]

Follow-up Comment #32, bug #49523 (project octave):

@Marco: Is it possible to pick the runtime parameters such as the
initialization vector v0 and the maximum number of iterations is such that at
least some of the returned values are NaN?  I know you have initialized both
of those items, but I wonder whether we should attempt to optimize those, or
maybe we should relax the tests.  For example, this is a failing test


A = toeplitz ([-2, 1, zeros(1, 8)]);
 A = kron (A, eye (10)) + kron (eye (10), A);
 opts.v0 = (1:100)';
 opts.maxit = 3;
 warning ("off", "Octave:eigs:UnconvergedEigenvalues", "local");
 d = eigs (A, 4, "lm", opts);
 assert (d(2:4), [NaN; NaN; NaN]);
!!!!! test failed
ASSERT errors for:  assert (d (2:4),[NaN; NaN; NaN])

  Location  |  Observed  |  Expected  |  Reason
    (1)         -7.365        NaN        'NaN' mismatch


What if we relaxed the conditions for the assert so that it was


assert (d(3:4), [NaN; NaN]);


This would still verify that unconverged Ritz values are returned as NaN, but
wouldn't require that exactly 3 Ritz values be unconverged.


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