[Octave-bug-tracker] [bug #54179] sparse/eigs.m test failure

[Andrew Janke]

Follow-up Comment #6, bug #54179 (project octave):

Under Octave 4.4.0 built against arpack 3.6.1 on macOS 10.13.5:

If I take the following test in eigs.m at lines 1439 through 1446:


%! A = toeplitz ([0, 1, zeros(1, 8)], [0, -1, zeros(1, 8)]);
%! A = kron (A, eye (10)) + kron (eye (10), A);
%! Afun = @(x) A * x;
%! opts.v0 = (1:100)';
%! opts.maxit = 5;
%! warning ("off", "Octave:eigs:UnconvergedEigenvalues", "local");
%! d = eigs (Afun, 100, 4, "lm", opts);
%! assert (d(3:4), [NaN+1i*NaN; NaN+1i*NaN]);


and decrease opts.maxit from 5 to 4, then the test passes.


octave:12> test eigs
PASSES 182 out of 182 tests


If I decrease opts.maxit further to 3, I get a different error, `eigs: error
-14 in dneupd`:


octave:10> test eigs
***** testif HAVE_ARPACK
 A = toeplitz ([0, 1, zeros(1, 8)], [0, -1, zeros(1, 8)]);
 A = kron (A, eye (10)) + kron (eye (10), A);
 Afun = @(x) A * x;
 opts.v0 = (1:100)';
 opts.maxit = 3;
 warning ("off", "Octave:eigs:UnconvergedEigenvalues", "local");
 d = eigs (Afun, 100, 4, "lm", opts);
 assert (d(3:4), [NaN+1i*NaN; NaN+1i*NaN]);
!!!!! test failed
eigs: error -14 in dneupd


This seems to agree with your analysis.

I am no math expert, so I am unable to evaluate these numbers as to
correctness.

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