#18972: twographs and Seidel switching
-------------------------------------+-------------------------------------
Reporter: dimpase | Owner:
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.9
Component: graph theory | Resolution:
Keywords: | Merged in:
Authors: | Reviewers: Nathann Cohen
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/dimpase/seidelsw | a3362414d8710523b1a7f118a96fb4617be36637
Dependencies: #18960, #18948, | Stopgaps:
#18988, #18991, #18986, #19018, |
#19019 |
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Comment (by dimpase):
Replying to [comment:95 ncohen]:
> > > - `T.is_t_design(k=3)` -- use `is_uniform`.
> >
> > I cannot, I need to test that it is a 2-design with blocks of size 3.
>
> `T.is_t_design(k=3)` is *equivalent* to `is_regular+is_uniform(k=3)`.
I don't call `is_t_design()` this way! I also set `t=2`. And surely
enough, it's a different story:
{{{
sage: T = IncidenceStructure([[0,1,2],[3,4,5]])
sage: T.is_t_design(t=2,k=3)
False
}}}
You might be confused by the terminology difference that I already
explained, that regularity of two-graphs and of hypergraphs are different
notions.
In fact, this term is hugely overused in maths in general; there are
regular maps, regular rings, regular sequences, regular graphs (which in
algebraic are totally different animals from regular (hyper)graphs),
regular points, etc etc etc...
>
> {{{
> sage: T = IncidenceStructure([[0,1,2],[3,4,5]])
> sage: T.is_t_design(k=3)
> True
> sage: T.is_t_design(k=3,return_parameters=True)
> (True, (1, 6, 3, 1))
> }}}
>
> Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/18972#comment:99>
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