On Wed, Dec 05, 2012 at 10:45:13AM -0800, Travis Scrimshaw wrote:
> Hey Andrew,
> It sounds more like you want to use a spare matrix (or even just a
> dictionary with a tuple as the key) and fill in entries as you compute
> them.
A sparse matrix would probably not work, as you can't make difference
between a coefficient that has been computed and is zero, and a not
computed coefficient.
I guess we need both; morphism implemented as matrices, and morphisms
implemented as "lazy matrices", and we should share as much as
possible between the two.
Andrew: please keep up implementing such things! Don't worrying too
much about the design; just make it as straightforward as
possible. When the infrastructure will be in place, it should be easy
to cleanup the things before getting them into Sage.
Btw: Hom(F, G, C) models the set of all morphisms from F to G in the
category C. By default, C is the meet of the categories of F and G. Of
course, for most categories one can't do much with that. But there
certainly are categories where we can or could and would want to:
- Hom(V, W, VectorSpaces)
- Hom(V, W, A-modules)
- Hom(F, G, Groups)
Cheers,
Nicolas
--
Nicolas M. Thiéry "Isil" <nthi...@users.sf.net>
http://Nicolas.Thiery.name/
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