#11735: Bug in is_chordal
----------------------------+-----------------------------------------------
Reporter: ncohen | Owner: tbd
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.7.2
Component: graph theory | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author: Nathann Cohen
Merged: | Dependencies:
----------------------------+-----------------------------------------------
Changes (by ncohen):
* status: new => needs_review
* component: PLEASE CHANGE => graph theory
Old description:
> As reported by Jon on sage-devel [1], the current implementation of
> is_chordal is incorrect. Given a vertex v adjacent to x and y (x and y
> being non-adjacent), a shortest path between x and y in G-v does not
> necessarily avoid the neighbors of v. Clearly.
> Well, with this patch the shortest path is computed in the graph G with v
> and all its neighbors removed with the exception of x and y, so that it
> can not happen again.
>
> Besides, as it is almost free to check that the certificate is indeed a
> hole, this patch adds a test just in case `:-)`
>
> Nathann
>
>
> [1] https://groups.google.com/d/topic/sage-support/rU1VTz1Ou_I/discussion
New description:
As reported by Jan on sage-devel [1], the current implementation of
is_chordal is incorrect. Given a vertex v adjacent to x and y (x and y
being non-adjacent), a shortest path between x and y in G-v does not
necessarily avoid the neighbors of v. Clearly.
Well, with this patch the shortest path is computed in the graph G with v
and all its neighbors removed with the exception of x and y, so that it
can not happen again.
Besides, as it is almost free to check that the certificate is indeed a
hole, this patch adds a test just in case `:-)`
Nathann
[1] https://groups.google.com/d/topic/sage-support/rU1VTz1Ou_I/discussion
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11735#comment:1>
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