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[Octave-bug-tracker] [bug #53719] eigs delivers wrong result in case of

From: Marco Caliari
Subject: [Octave-bug-tracker] [bug #53719] eigs delivers wrong result in case of complex valued general eigenvalue problem
Date: Tue, 24 Apr 2018 05:04:03 -0400 (EDT)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:59.0) Gecko/20100101 Firefox/59.0

Update of bug #53719 (project octave):

                  Status:             In Progress => Patch Submitted        


Follow-up Comment #5:

I decided for two patches. The first is about the segmentation fault.
Moreover, it fixes some conditions in the subfunction select in eigs.m. It
should certainly be applied (eigs1.diff).

The second changes the switch between using ARPACK or eig inside eigs.m.
Unfortunately, it was not as easy as I thought in comment #3. In fact, we
should compare p and rows (a). By default, p is 2 * k, but it can be
overwritten by opts.p. I also changed a lot of BIST tests in order to really
use ARPACK and not eig. Since the default number of eigenvalues is 6, and the
default Krylov dimension is 2 * 6, I forced eigs to use eig when rows (a) < 13
(it was rows (a) < 9). This second patch (eigs2.diff) needs an accurate review
(we should be sure that all tests pass again on different platforms) and does
not solve the undetected ill-conditioning of the problem in this bug report.

When eig is used, the output argument flag is set to 0. What about setting it
to -0 in order to know when eig was used instead of ARPACK?

(file #44003, file #44004)

Additional Item Attachment:

File name: eigs1.diff                     Size:2 KB
File name: eigs2.diff                     Size:11 KB


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