On Fri, Mar 04, 2011 at 02:44:06AM -0800, Volker Braun wrote:
> One problem is that we don't have toric morphisms implemented yet (Though
> the convex geometry FanMorphism is done). Partly because I have no idea
> how the category framework should be used to implement them. So we can't
> implement the summand_projection yet.
summand_projection can return a plain python function. Actually, this
is what sage.sets.cartesian_product.CartesianProduct.summand_projection
does (in that case, it just delegates the work to the summand_projection
method of the elements).
That being said, building a morphism from a python function is as easy as:
sage: F = ZZ
sage: G = QQ
sage: f = sage.categories.morphism.SetMorphism(Hom(F, G,
category=Semigroups()), lambda x: x/2)
sage: f(3)
3/2
(Note: Simon King is currently working hard on morphisms and in
particular their documentation, so the situation should improve!).
> Is there anything wrong with just overriding cartesian_product to return
> the Cartesian product without the extra structure for now, and then
> implement the extra structure later?
As long as it is documented as a missing feature (typically by showing
the warning that TestSuite should issue), that sounds ok.
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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