#18972: twographs and Seidel switching
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Reporter: dimpase | Owner:
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-6.9
Component: graph theory | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/dimpase/seidelsw | 758da33a4bd616f97e2b9748236c0d866fb8f79d
Dependencies: #18960, #18948 | Stopgaps:
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Comment (by ncohen):
Hello,
> > I already made comments on the code of `seidel_switching`,
> You said there that Graph.vertices() is a plain list, and I should
> make it a set, or something? (I guess a dictionary, as I need to know
> the original indices)
>
> It's a usual operation, find positions of vertices... E.g.
> how do you construct subgraphs without essentially doing this?
I was refering to point 5 of [comment:1]. It contains code.
> >and you need to document what a `twograph_descendant` is.
>
> it's the composition of two documented functions, isn't it enough?
Neither `twograph_descendant` nor `TwoGraph.descendant` define what a
descendant is.
> It is a hell of lot faster for cases with more than 100 vertices, say.
`O(n^2)` vs `O(n^3)`.
We have very fast functions in modules, too. For hyperbolicity, for vertex
separation, for.. Well, a lot of things. It can be made much faster,
however, if you rewrite it to use `seidel_switching` and rewrite
`seidel_switching` with the code of [comment:1].
> Did you see the
[http://git.sagemath.org/sage.git/diff/src/sage/graphs/generators/families.py?id=5115728f80aa95f87a272feec999e317ccdffba4&id2=edb1b0870d25373a1cf8def52c5fe3159245f59d
patch for Chang graphs]? Do you think it is useless and should be removed?
It is unrelated to my point: this is nice indeed, but it merely uses
`seidel_switching`, and that's it.
> I don't know how to rebuild the database, so that it is available as
Look for {{{(275, 112, 30, 56)}}} in `strongly_regular_db.pyx`.
Nathann
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Ticket URL: <http://trac.sagemath.org/ticket/18972#comment:28>
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