On Wed, Aug 26, 2009 at 2:39 PM, Jason Grout<jason-s...@creativetrax.com> wrote: > > Nathann Cohen wrote: >>> Yes, you can use indexation like some_oovar[i] or some_oofun[i] >>> (probably with several indexes, or negative ones that are start from >>> array end), however, I think it should be avoided if possible (you'd >>> better split your oovar into several >>> oovars).http://www.openopt.org/FuncDesignerDoc#Some_issues_to_be_aware >> >> I sent a message on sage-support to know to which extent I could use >> multivariate Polynomials in Sage to represent constraints and Linear >> functions, but it seems to be troublesome... This said, there is no >> way for me to use Linear Programming if I can not use indexed >> variables... At the moment, even though the syntax could be >> tremendously improved, I can use any hashable Sage object as a >> variable, and most of the time in Graph theoretic function my >> variables are edges, vertices, or arbitrary tuples and strings. >> Anyway, most of the Linear Programs are generated from graphs and I >> have to find a way to let a computer create as many variables as >> possible :-/ >> The current syntax, though, is not nearly satisfying. >> > > I should mention that at various times, people have proposed that you > could create symbolic variables x[1], x[2], etc. As far as I know, > these proposals have just been ideas and have never been implemented or > experimented with. > > Maybe we could make x[1] a symbolic variable automatically. We would > have to make an indexing function for symbolic variables that would > return a symbolic variable that would be cached somewhere (so that x[1] > always referred to the same variable). That would also give us nested > indices, as x[1][1] would take a symbolic variable x, create a new one > x[1], and then x[1] would create another symbolic variable x[1][1]. >
That sounds pretty easy to implement by defining __getitem__ for symbolic variables, and making it cache its answer using a dictionary. Should one only allow x[integer] or more generally x[anything hashable]? William --~--~---------~--~----~------------~-------~--~----~ To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
