LatticePoset: Add iterator over isomorphic sublattices

[jm58660]

This patch will add a function to iterate over isomorphic sublattices; compare to isomorphic_subposets_iterator().

Implementation is trivial. Better ideas are welcome.

CC: @fchapoton

Component: combinatorics

Author: Jori Mäntysalo

Branch/Commit: 05efd9a

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/21635

[jm58660]

Branch: u/jmantysalo/isom-sublattices-iterator

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

2765937

Crosslinks.

[sagetrac-git]

Commit: 2765937

[jm58660]

New commits:

1d4c4f1	Add isomorphic_sublattices_iterator().
2765937	Crosslinks.

---

New commits:

1d4c4f1	Add isomorphic_sublattices_iterator().
2765937	Crosslinks.

[tscrim]

comment:5

What happens when this is given a poset which is not a lattice? Should it fail? From looking at the code, it seems like it would start going through and then sublattice would be the point of failure. Also, this makes sense for a general poset, so could we move it up to there?

[jm58660]

comment:6

This (indirectly) calls self.meet() and self.join(), hence does not make sense to move function to posets.

In this implementation other can really be any poset, but if it is not a lattice by structure, the function will return empty list (i.e. instantly raise StopIteration). How should this behave?

[tscrim]

comment:7

Replying to @jm58660:

This (indirectly) calls self.meet() and self.join(), hence does not make sense to move function to posets.

Ah, yes. I agree.

In this implementation other can really be any poset, but if it is not a lattice by structure, the function will return empty list (i.e. instantly raise StopIteration). How should this behave?

You should add an example showing this happens and perhaps change the input to say - ``other`` -- finite poset.

One other little detail, remove the period in the .. SEEALSO:: blocks.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

05efd9a

Check for being lattice, not any poset.

[sagetrac-git]

Changed commit from 2765937 to 05efd9a

[jm58660]

comment:9

I thinked slightly more about this. We can always loose restrictions from a lattice to a poset, and so this code wants exactly lattices. It may also help if I try to invent some better way to list isomorphic sublattices.

[jm58660]

comment:10

Just pinging. Is this solution (requiring other to be a lattice) OK?

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:11

This is good with me.

[vbraun]

Changed branch from u/jmantysalo/isom-sublattices-iterator to 05efd9a