[Octave-bug-tracker] [bug #53700] eigs test failure related to ARPACK generating real NaN rather than complex NaN+1i*NaN

[Dan Sebald]

URL:
  <http://savannah.gnu.org/bugs/?53700>

                 Summary: eigs test failure related to ARPACK generating real
NaN rather than complex NaN+1i*NaN
                 Project: GNU Octave
            Submitted by: sebald
            Submitted on: Thu 19 Apr 2018 04:50:06 PM UTC
                Category: Test Suite
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Regression
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: GNU/Linux

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Details:

I have one test failing on a very up-to-date Ubuntu 18.04 with KDE (not that
the latter matters, I suppose), and it seems along the lines of this bug
report. If it isn't the same, I'll create a separate bug report.

I will isolate just the failing test:


octave:1> test eigs
***** testif HAVE_ARPACK
 A = magic (100) / 10 + eye (100);
 opts.v0 = (1:100)';
 opts.maxit = 10;
 warning ("off", "Octave:eigs:UnconvergedEigenvalues", "local");
 d = eigs (A, 10, "sm", opts);
 assert (d(10), NaN+1i*NaN);
!!!!! test failed
ASSERT errors for:  assert (d (10),NaN + 1i * NaN)

  Location  |  Observed  |  Expected  |  Reason
     ()           O            E         real != complex


and a more detailed breakdown


octave:2> A = magic (100) / 10 + eye (100);
octave:3> opts.v0 = (1:100)';
octave:4> opts.maxit = 10;
octave:5> d = eigs (A, 10, "sm", opts);
warning: eigs: Only 1 of the 10 requested eigenvalues converged
warning: called from
    eigs at line 265 column 18
octave:6> assert (d(10), NaN+1i*NaN);
error: ASSERT errors for:  assert (d (10),NaN + 1i * NaN)

  Location  |  Observed  |  Expected  |  Reason
     ()           O            E         real != complex
octave:6> d(10)
ans =  NaN
[snip]
octave:8> d
d =

   1.00000
       NaN
       NaN
       NaN
       NaN
       NaN
       NaN
       NaN
       NaN
       NaN


So, it appears that there is non-convergence but this is probably expected
behavior because the test is disabling the printout of warning messages about
non-convergence. It may be the only issue is that ARPACK is generating "real"
(float) values where another library is generating "complex" values. Perhaps
there is a change in recent versions of ARPACK, don't know. If you want me to
investigate further, I can.




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