Re: [PATCH 2/2] add permutation iterator
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- Subject: Re: [PATCH 2/2] add permutation iterator
- From: "S. Gilles" <sgilles@xxxxxxxxxxxx>
- Reply-to: myrddin-dev@xxxxxxxxxxxxxx
- Date: Tue, 2 Jan 2018 06:20:59 -0500
- To: myrddin-dev <myrddin-dev@xxxxxxxxxxxxxx>
- Cc: Ori Bernstein <ori@xxxxxxxxxxxxxx>
On 2018-01-01T23:16:29-0800, Ori Bernstein wrote: > Sorry for taking a while to review this. Overall, it looks pretty good, > just a few minor nits. I've already made them on my local branch, so > as long as they look good to you, I can push. > > [...] > > -- > Ori Bernstein (My apologies, anti-Reply-All instincts sent this to the wrong place the first time.) No objections on my part, and I agree with your expanded comments. Regarding the slice/iterable discrepancy, I think restricting this iterable to slices is not terrible. The other day I implmented a naive markov chain as an iterable, which exposes some more potential problems: - iterables do not necessarily return a bounded number of valp#s, - iterables do not necessarily return the same sequence when you call them multiple times. In light of that, I'm completely okay with that restriction. As to what I needed that iterator for: as part of my work I'm trying to find sequences of graph mutations μ such that μ(G) is graph-isomorphic to “G but with certain (‘frozen’) vertices relabeled so that the whole thing is rotated 90 degrees”. When such a μ is found, we can use it as a ‘map’ through a tetrahedron (G is the top two faces, μ(G) is the bottom two, μ tells us what happens in the interior). If we then do this to a bunch of tetrahedra, we can glue the tetrahedra together to form a triangulated 3-manifold M. Then, the information given by stapling all of the μs and Gs together allows us to examine (certain properties of) M by simple examining graphs. The properties depend on which G we started out with. Some parts of [0] are pretty readable, though the later sections get pretty technical. So anyway, in order to check μ, I needed a way to check whether two graphs were isomorphic, and the most naive way to do that is to permute [some of] the vertices in place and then check whether the sets of edges agree. [0]: https://arxiv.org/abs/1605.08297 -- S. Gilles
Re: [PATCH 2/2] add permutation iterator | Ori Bernstein <ori@xxxxxxxxxxxxxx> |
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