#14126: Count Number of Linear Extensions of a Poset
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Reporter: csar | Owner: sage-combinat
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-5.8
Component: combinatorics | Resolution:
Keywords: days45 | Work issues:
Report Upstream: N/A | Reviewers:
Authors: aschilling, nthiery, hivert | Merged in:
Dependencies: | Stopgaps:
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Comment (by ncohen):
Hellooooooooo !!
> Fair point. `cardinality()` doesn't seem to live in
`sage.combinat.posets.linear_extensions`, though. It looks like it comes
from the `FiniteEnumeratedSets` category.
Oh. Right. So it builds all linear extensions then counts them `-_-`
> Is it legitimate to give `LinearExtensionsOfPoset` a cardinality
function with an argument to choose between the
`_cardinality_from_iterator` from `FiniteEnumeratedSets` and counting
recursively? My understanding of how categories are meant to work does not
extend this far.
My understanding of categories is that when they prevent you from doing
something you need then categories should be changed to allow you to do
whatever you wanted to do in the first place.
Technically I do not think that categories would mind an optional argument
to .cardinality. I guess that they would not notice it, so that's all
good.
This being said, if you are at the Sage Days 45 right now Nicolas Thiery
should be around. And he's THE guy you should bug for anything related to
categories `:-P`
Nathann
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14126#comment:10>
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