#14297: is_strongly_regular does not handle complete graphs
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Reporter: azi | Owner: jason, ncohen, rlm
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-5.10
Component: graph theory | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Frédéric Chapoton | Merged in:
Dependencies: | Stopgaps:
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Comment (by ncohen):
> Eeeehm just checked in the book
(http://www.win.tue.nl/~aeb/2WF02/spectra.pdf page 123 lol) by Brower and
Haemers they exclude the complete graph and its complement as well.
Well, they are free to have their own opinion too. Mine is that I like to
consider them as strongly regular graphs. Now we can put whatever you want
in Sage, the one who agrees with a book is usually the one who is
acknowledged to be right, nowadays `:-P`
> I like gambling so we can toss a coin though I prefer to exclude
complete graphs.
>
> Also while we are at it:
>
> {{{
> 2293 degree = self.degree()
> 2294 k = degree[0]
> 2295 if not all(d == k for d in degree):
> 2296 return False
> 2297
> 2298 if self.is_clique():
> }}}
>
> is it perhaps better to call self.is_regular()? I would like that since
it somehow leaves any optimizations that is_regular *could* do and has the
added benefit that this method does not break for the EmptyGraph (corner
cases lol)
Oh. Well, then one would first have to take "any" vertex of the graph,
compute its degree, then call `is_regular` on it with this degree as
parameter. Otherwise it will call `self.degree()` twice. It's up to you !
Nathann
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14297#comment:9>
Sage <http://www.sagemath.org>
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