#17787: Wrong result returned by Graph.is_interval
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Reporter: ncohen | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.5
Component: graph theory | Keywords:
Merged in: | Authors: Nathann Cohen
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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It has been reported by Damian Bogdanowicz on sage-devel [1] that the
interval graph recognition agorithm returns a wrong result:
{{{
sage: Graph('GvGNp?').is_interval()
True
}}}
This graph is not an interval graph as it contains an asteroidal triple
(1,5,7).
The fix is rather short: some 'partial' pq-trees were handled like 'full'
ones and that was wrong. As an additional check, we get the expected [2]
number of interval graphs up to n=9:
Nathann
P.S.: The class, however, could definitely benefit from a more general
rewrite. Another ticket (already half-written) will adress that and make
the documentation and method names more explicit.
[1] https://groups.google.com/forum/#!topic/sage-combinat-
devel/DnULBrlkgBc
[2] http://oeis.org/A005975
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Ticket URL: <http://trac.sagemath.org/ticket/17787>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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