[Octave-bug-tracker] [bug #45153] eigs returning an incorrrect number of eigenvalues

[Marco Caliari]

Update of bug #45153 (project octave):

                  Status:               Confirmed => Patch Submitted        

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Follow-up Comment #8:

Finally, I have a patch to the stable branch. I think there was already a
tentative to give the exact number of required eigenvalues, but not working,
and buggy in fact. See the new test containing isnan. The same test showed a
differente bug in ARPACK itself (
https://github.com/opencollab/arpack-ng/issues/58).
I also fixed bug #47236, somehow related. Now eigs returns the correct number
of eigenvalues and "essentially" in the same order for the calls [v1,d1] =
eigs(...) and d2 = eigs(...). Some discrepancies are still possible, however,
when conjugate pairs are present. For instance, it is possible that


diag(d1)
ans =

   0.88029 + 0.30282i
   0.88029 - 0.30282i
  -0.69077 + 0.75447i
  -0.69077 - 0.75447i
  -1.12180 + 0.25552i


and


d2
ans =

  -1.12180 - 0.25552i
  -1.12180 + 0.25552i
   0.88029 + 0.30282i
   0.88029 - 0.30282i
  -0.69077 - 0.75447i


This is ARPACK. I also allowed p to take the value n (as in Matlab and
ARPACK), since it can speed up the convergence.
Please revise my patch.

(file #40201)
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Additional Item Attachment:

File name: eigs_stable.patch              Size:24 KB


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