On Sat, Feb 18, 2012 at 01:39:31PM -0800, Anne Schilling wrote:
> Having this as an input in Poset was my very first suggestion.
Was it? I had understood you wanted to change the linear extension of
a poset, and I had (mis?)interpreted that relabeling a poset would be
a building block of the algorithmic, which would create a bunch of
copies of the same poset with a different linear extension. This did
not feel reasonable. On the other hand, specifying the default linear
extension for a Poset is certainly a natural feature!
In any cases ...
> But now my inclination is actual different. I think the real culprit
> that throws me off in the applications I have in mind are the methods
>
> def _vertex_to_element(self,vertex):
>
> and
>
> def _element_to_vertex(self,element):
>
> in /combinat/posets/posets.py, which assign the integers 0,1,2,....,n-1 to the
> elements in the poset. The linear extension of a given poset is in fact set
> to the
> identity (which is what I really want)
The fact that Posets are implemented by using a backend _hasse_diagram
where the vertices are labelled 0,...,n-1 is an internal
implementation detail, and you don't want to rely on it; well, except
maybe for optimization purposes, but in any cases you do not want to
expose it to the user. Besides it's best if all features work
uniformly independently of the names of the vertices of the poset.
> Also, I tend to think of linear extensions as permutations rather
> than lists of poset elements.
Just to make sure: here you mean permutation as in PermutationGroup,
right?
This is an interesting point, though fairly independent on the
previous one, since we can now have permutations of any set (thanks
Mike!). Does the multiplicative structure of permutations play a role?
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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