On Sat, Feb 11, 2012 at 11:11:31AM -0800, Anne Schilling wrote:
> > If yes, then maybe something like:
> >
> > P = Poset(...)
> > Q = P.enumerated_by(<some linear_extension of P>)
>
> Yes, in my last e-mail, I already sent the code for this (what I
> called from_linear_extension you call enumerated_by):
I know, I was just suggesting a name for it.
> Well, at the end it will give a graph on the set of all linear extensions.
> Promotion (or the generalized promotions as well) for example, take as input
> a poset P
> and out comes another poset (with its vertices relabeled). It is most
> convenient to program this directly on the linear extension of P. But
> in Sage there is no class for linear extensions and as far as I can see
> no method that converts between linear extensions and actual posets.
Thanks for the clarification. Let me restate it to check I am having
it right. You have a poset, say:
sage: P = Poset((divisors(30), attrcall("divides")))
and then you want to manipulate a bunch of linear extensions of that
poset like::
sage: l1 = [1, 5, 3, 2, 10, 6, 15, 30]
sage: l2 = [1, 2, 3, 5, 6, 15, 10, 30]
...
Then, to apply an operation `blah` on a linear extension of P, you
need both P and the linear extension. A first approach is to put blah
as a method of P::
sage: P.blah(l1)
...
Another approach is to have a class LinearExtensionOfPoset so that one
can do::
sage: l1 = LinearExtensionOfPoset(P, [1, 5, 3, 2, 10, 6, 15, 30])
sage: l1.blah()
...
The choice depends mostly on how many methods one wants to have: for
more than two or three, it is indeed more reasonable to not pollute
P's namespace.
By the way, one might event want to have a class LinearExtensionsOfPoset::
sage: L = LinearExtensionsOfPoset(P); L
The set of all linear extensions of L
sage: L.cardinality()
...
sage: L.an_element():
...
And then one could do something like:
sage: L.promotion_graph()
A variant of the above would be to have L be a facade parent, and call
the operations like `blah` as:
sage: L.blah(l1)
> I already implemented my algorithms. I just do not know where to put them
> in /combinat/posets.py since there is no class for linear extensions.
> For their analogs on posets it is clear, but it is useful to have the helper
> methods on linear extensions directly.
I was precisely asking about (the names of) those helper methods to
see if it was worth creating that new class LinearExtensionOfPoset.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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