#18972: twographs and Seidel switching
-------------------------------------+-------------------------------------
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 | 449a23ec5b0305fc2f7132bdd38ba0923ec01b89
Dependencies: #18960, #18948 | Stopgaps:
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Comment (by dimpase):
Replying to [comment:28 ncohen]:
> > > 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.
>
I changed `seidel_switching()` in the way you propose. As the function
returns a new
graph, I needed to use `deepcopy(self)` (`copy(self)` is not enough).
Perhaps there is a better way...
> > >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.
OK, oops, fixed in the next commit.
>
> > 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.
>
OK, perhaps I misunderstood your point.
> > 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`.
OK, thx, fixed.
----
New commits:
||[http://git.sagemath.org/sage.git/commit/?id=c4269aeae44bbd64afbdee96f04fb120d73f0de1
c4269ae]||{{{doc and srg DB fixes}}}||
||[http://git.sagemath.org/sage.git/commit/?id=449a23ec5b0305fc2f7132bdd38ba0923ec01b89
449a23e]||{{{improving seidel_switching()}}}||
--
Ticket URL: <http://trac.sagemath.org/ticket/18972#comment:31>
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