#14297: is_strongly_regular does not handle complete graphs
-------------------------------------+--------------------------------------
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 azi):
Replying to [comment:11 ncohen]:
> Hellooooooooo !!!
>
> > Luckily we don't have as many books saying different things as
religions do :-)
>
> Yeah ? Well, try to publish a paper with you own notations for
everything and see if it goes through. We don't have many religions
because only one religion is allowed to exist `:-P`
That's the proper way to do it.. Isn't there only one God after all?
>
> > Anyways, I personally like to have it that way because then there are
other theorems for strongly regular graphs that follow naturally. For
example a strongly regular graphs has precisely three distinct eigenvalues
(which does not hold for the empty graph and complete graph)
>
> Oh ? I didn't know that !
Yey,yes there are some nice results like that for SR graphs.
>
> > That said I don't care what we do with this as long as its fine with
you guys. Hence I let you and Frederic decide!
>
> Well, if you have a nice theorem like that, after all... So, Frederic ?
>
> > You got a point I overlooked that! BUT we can at least remove the
is_clique part and check if the degree is order()-1 once we know its
regular right??
>
> Ahahahah. And what if is_clique just computes the number of edges, and
if the number of edges is cached ? `:-P`
LOL
>
> I don't know if it is, though. But calling `.size()` probably does not
list all edges..... At least I hope !
Of course it does and it does so in a fancy manner
{{{
2001 if self.loops(None):
2002 if self.multiple_edges(None):
2003 for j in self.iterator_verts():
2004 if self.has_edge(j, j, None):
2005 k += len(self.get_edge_label(j, j))
2006 else:
2007 for j in self.iterator_verts():
2008 if self.has_edge(j, j, None):
2009 k += 1
2010 i = (i - k) / 2
2011 return i + k
}}}
Seems like we can add this to a new ticket? Or am I missing a detail that
makes this code actually efficient?
>
> Nathann
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14297#comment:12>
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