Hi Nathann,
On Mon, Aug 31, 2009 at 5:59 AM, Nathann Cohen<nathann.co...@gmail.com> > Is there a way in Sage to define a Formal sum ? Something like > sum( a_i, i \in [0,...5] ) or even worse, sum(a_e, e\in g.edges()) for > g a graph, etc. For formal or symbolic sum, you need to make it a SFunction sub-class of new symbolics. Unfortunately, it is yet to be implemented/ported to the new symbolics and it would be great if you could do this, See this ticket for related discussion http://trac.sagemath.org/sage_trac/ticket/3587 I think, symbolic sum implementation would be very similar to symbolic "integrate" implementation. Please have a look at the patch http://trac.sagemath.org/sage_trac/ticket/6465 > I insist it should be a "formal sum", as it should not return sum > ( [a_i for i in range(6) ] ) or sum( [a_e for e in g.edges() ] ) , but > rather an abstract formula for this. It could be evaluated at any > moment, giving different results if the a_i have changed or if the > graph has changed meanwhile. In the _eval_ method of the new class, you can decide on the situation where you want to evaluate explicitly or leave it symbolic. If you want to leave it symbolic then just "return None" . Cheers, Golam --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
