[Octave-bug-tracker] [bug #41305] error: eigs: error -14 in dneupd

[Mike Miller]

Update of bug #41305 (project octave):

                  Status:                    None => Confirmed              

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Follow-up Comment #1:

Thanks for your bug report. I don't have Octave 3.4.2 to test with at the
moment. However, with 3.6.4 I actually get the reverse behavior, are you sure
you didn't swap those two rand initializers?

Someone with more insight into the eigs algorithm than me will have to comment
on this, but here's what I see with Octave 3.8.0 (same as with 3.6.4). Asking
for more eigenvalues works, but limiting it to 1 or 2 makes arpack fail to
return any in this case.


octave:1> function x = func(n)
> x = rand (n);
> x(x < 0.9) = 0;
> x(x != 0) = rand (size (x(x != 0))) - 0.5;
> endfunction
octave:2> rand ("state", 137); w = func (200); eigs (w, 1)
error: __eigs__: eigs: error -14 in dneupd
error: called from:
error:   /usr/share/octave/3.8.0/m/sparse/eigs.m at line 260, column 18
octave:2> rand ("state", 137); w = func (200); eigs (w, 2)
error: __eigs__: eigs: error -14 in dneupd
error: called from:
error:   /usr/share/octave/3.8.0/m/sparse/eigs.m at line 260, column 18
octave:2> rand ("state", 137); w = func (200); eigs (w, 3)
ans =

  -0.12943 + 1.26169i
  -0.12943 - 1.26169i
  -1.25249 - 0.18251i



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