Re: Cancel[] and finite symbolic sums ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg102791] Re: [mg102763] Cancel[] and finite symbolic sums ?*From*: "David Park" <djmpark at comcast.net>*Date*: Thu, 27 Aug 2009 06:35:26 -0400 (EDT)*References*: <15915821.1251288036966.JavaMail.root@n11>

You could try something like this: Sum[W*Subscript[b, k], {k, 1, N}]/W MapAt[Part[%, 1] # &, Part[%, 2], 1] David Park djmpark at comcast.net http://home.comcast.net/~djmpark/ From: Andre Holzner [mailto:andre.holzner at gmail.com] Dear experts, I wonder what I'm doing wrong here... I try to simplify the following expression: [Sum[W * Subscript[b, k], {k, 1, N}]/W by doing Cancel[Sum[W * Subscript[b, k], {k, 1, N}]/W] it looks like Mathematica just returns me the original expression: Sum [W*Subscript[b, k], {k, 1, N}]/W When I try a sum over b instead of Subscript[b, k], it seems to work as expected: Cancel[Sum[W * b, {k, 1, N}]/W] gives: b*N Any ideas what I'm doing wrong ? thanks, Andre