#8756: random segfault in planarity.pyx test
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Reporter: was | Owner: jason, ncohen, rlm
Type: defect | Status: new
Priority: blocker | Milestone: sage-4.4.1
Component: graph theory | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by jason):
Whoever investigates this, here was another segfault in the planarity
testing that was fixed a while ago: #4509
I hope they're not related, but it might be something to keep in mind if
someone is investigating the issue (maybe someone can try *just* running
the code on connected graphs, or just on disconnected graphs to try to
narrow things down). In that case, according to John Boyer (the author of
the C code we use):
"I'll say up front that you're absolutely right that my reference
implementation does not pay any real attention to isolated vertices as
they have nothing really to do with the correctness of the algorithm."
The problem in that case was that we were segfaulting on graphs with
vertices of degree zero (i.e., isolated vertices). I wonder if that is
causing a problem somewhere else in his code, or if somehow we are seeing
the same issue again (was that code changed recently?).
One possible option is to upgrade to John Boyer's latest complete rewrite
of planarity testing code, of which he says:
"the only code on which I am comfortable with claiming support for
disconnected graphs is the new "version 2.0" code.
"The reason I say it is possibly fortunate is that it should be precious
little effort for you to consider adopting this new code since I kept
backwards compatibility at a high priority. You are quite unlikely to have
done anything that is not supported under the new code, though I can help
you if there are *any* issues. Best of all, you can actually get the code
because I've made it publicly available from a Google Code project.
http://code.google.com/p/planarity";
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8756#comment:6>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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