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

[Dmitri A. Sergatskov]

Follow-up Comment #23, bug #49523 (project octave):

I also get different test failures depending on the blas version used:

LD_PRELOAD=/usr/lib64/libopenblas.so.0 ./run-octave -f -q --no-gui
octave:1> test eigs
***** testif HAVE_ARPACK
 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

LD_PRELOAD=/usr/lib64/atlas/libsatlas.so ./run-octave -f -q --no-gui
octave:1> test eigs
***** testif HAVE_ARPACK
 A = magic (100) / 100 + eye (100);
 opts.v0 = (1:100)';
 opts.maxit = 1;
 warning ("off", "Octave:eigs:UnconvergedEigenvalues", "local");
 d = eigs (A, 4, "sm", opts);
 assert (d(3:4), [NaN+1i*NaN; NaN+1i*NaN]);
!!!!! test failed
ASSERT errors for:  assert (d (3:4),[NaN + 1i * NaN; NaN + 1i * NaN])

  Location  |  Observed  |  Expected  |  Reason
    (1)      1+1.783e-14i   NaN+NaNi     'NaN' mismatch

LD_PRELOAD=/usr/lib64/libblas.so.3 ./run-octave -f -q --no-gui
octave:1> test eigs
***** testif HAVE_ARPACK
 A = toeplitz ([0, 1, zeros(1, 8)], [0, -1, zeros(1, 8)]);
 A(1, 1) = 1;
 A = kron (A, eye (10)) + kron (eye (10), A);
 opts.v0 = (1:100)';
 opts.maxit = 1;
 warning ("off", "Octave:eigs:UnconvergedEigenvalues", "local");
 d = eigs (A, 4, "sm", opts);
 assert (d(3:4), [NaN; NaN]);
 assert (imag (d(3:4)), [0; 0]);
!!!!! test failed
ASSERT errors for:  assert (d (3:4),[NaN; NaN])

  Location  |  Observed  |  Expected  |  Reason
    (1)        0.067993       NaN        'NaN' mismatch

Those are 100% reproducible.
I use 
arpack-devel-3.5.0-4.fc27.x86_64
arpack-3.5.0-4.fc27.x86_64
(same as fedora buildbots)

Dmitri.


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