#16370: OA(k,n) strongly regular graphs
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Reporter: | Owner:
ncohen | Status: needs_review
Type: | Milestone: sage-6.3
enhancement | Resolution:
Priority: major | Merged in:
Component: graph | Reviewers:
theory | Work issues:
Keywords: | Commit:
Authors: | e3c1c2180178c94d883db945dc33f2b457330cbc
Nathann Cohen | Stopgaps:
Report Upstream: N/A |
Branch: |
u/ncohen/16370 |
Dependencies: |
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Comment (by vdelecroix):
Replying to [comment:22 ncohen]:
> Yo !
>
> > Yes: this ticket should not go without a `graphs.IntersectionGraph`.
And intersection graphs of non-trivial BIBD are regular graph. So it is
worth to have them at least in the doc of `graphs.IntersectionGraph`.
>
> Intersection graphs are something we should add, but it is not a
dependency of this ticket so it will be done elsewhere.
All right. But as Brouwer said himself in his answer it would be much more
consistent to have
{{{
sage: designs.MyPreferedDesign(x,y,z).block_intersection_graph()
}}}
and not
{{{
sage: graphs.BlockIntersectionGraphFromMyPreferedDesign(x,y,z)
}}}
> > * for TD(k,n): lambda=(k-1)(k-2)+n-2, mu=k(k-1)
>
> I added a line about that in the construction of the orthogonal array
graph, see commits.
hum: k=k(n-1)
I see two more obstructions right now:
- having a function with two integers as input makes anybody think that
there is a unique graph associated with all OA(k,n). I do not believe that
this is True. It must be very clear in the documentation.
- the function `designs.orthogonal_array` might not give the same output
between two releases of Sage. So if somebody starts working on OA(5,19)
and loves it and find out that three months after her graph disappear, it
would be a disaster.
Vincent
--
Ticket URL: <http://trac.sagemath.org/ticket/16370#comment:27>
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