#13546: Bug in is_perfect
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Reporter: azi | Owner: jason, ncohen, rlm
Type: defect | Status: needs_review
Priority: critical | Milestone: sage-5.7
Component: graph theory | Resolution:
Keywords: is_perfect,graph theory | Work issues:
Report Upstream: N/A | Reviewers: Jernej Azarija,
Sébastien Labbé
Authors: Nathann Cohen | Merged in:
Dependencies: #8952 | Stopgaps:
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Comment (by ncohen):
> Anyhow. I am aware of the sparse6 issue but in my opinion that is an
issue of how we currently handle sparse6 strings! So if we enforce the
simplicity rule in is_perfect then at some point someone will perhaps get
annoyed and want an option of the form
Right now there is no problem with sparse6 strings, because the functions
does not check whether the graph ALLOWS loops and multiple edges, but
whether it HAS some. So the exception is not raised for sparse6 string,
and is only raised if there is a loop in the graph, or multiple edges.
> As far as I see, the patch need not remove loops and multiple edges from
the complement now?
It is still needed, for instance for graphs coming from sparse6, because
even though they contain no multiple edges and loops they allow it. So the
complement will have multiple edges.
Actually, the problem is probably that taking the complement of a graph
that allows loops will add loops and multiple edges to the graph, and I
don't really think that's a good behaviour.
Nathann
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13546#comment:24>
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