#11735: Bug in is_chordal
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Reporter: ncohen | Owner: tbd
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.8
Component: graph theory | Keywords:
Work_issues: | Upstream: N/A
Reviewer: David Coudert | Author: Nathann Cohen
Merged: | Dependencies:
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Comment(by ncohen):
Well, this graph clearly contains a long hole (induced cycle). Sage can
find it too, with the "certificate" flag :
{{{
sage: G.is_chordal(certificate = True)
(False, Subgraph of (): Graph on 50 vertices)
sage: G.is_chordal(certificate = True)[1].show()
}}}
I mean, a graph is chordal if it contains an induced long cycle, and if
you build a cycle of triangles it will of course contain a large induced
cycle : the triangles offer no protection against that (just take two
vertices that are very far away from each other, and compute a shortest
path between them. As any shortest path, this path is induced, and the
same way you can obtain an induced cycle).
Nathann
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11735#comment:8>
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