Re: Sum

*To*: mathgroup at smc.vnet.net*Subject*: [mg55232] Re: [mg55175] Sum*From*: DrBob <drbob at bigfoot.com>*Date*: Thu, 17 Mar 2005 03:29:08 -0500 (EST)*References*: <200503161035.FAA23742@smc.vnet.net> <opsnqm72iyiz9bcq@monster.ma.dl.cox.net>*Reply-to*: drbob at bigfoot.com*Sender*: owner-wri-mathgroup at wolfram.com

>> If the result weren't infinite, that would be a good idea. Oops, I take that back. It would almost always be a bad idea, so I don't know why Evaluate isn't automatic. Bobby On Wed, 16 Mar 2005 10:10:40 -0600, DrBob <drbob at bigfoot.com> wrote: > Sum tried to simplify BEFORE substituting the value of x. If the result weren't infinite, that would be a good idea. But in this case, it's not. But there's a simple fix: > > x = Exp[-k] > Sum[Evaluate@x, {k, 0, Infinity}] > > E^(-k) > E/(-1 + E) > > Bobby > > On Wed, 16 Mar 2005 05:35:51 -0500 (EST), mjumbo <mjumbo at nm.ru> wrote: > >> Can sombody explain me why >> >> Sum[Exp[- k], {k, 0, Infinity}] >> >> gives the correct result, while the following (imho equivalent) statements >> >> x = Exp[-k] >> Sum[x, {k, 0, Infinity}] >> >> don't? What should I do to make it work? It is rather vexing to copy/paste long expressions instead of using short placeholders like x. >> __________ >> www.newmail.ru -- Íîâàÿ Ïî÷òà: âñå ïî-íîâîìó. >> >> >> >> > > > -- DrBob at bigfoot.com

**Follow-Ups**:**Re: Re: Sum***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>

**References**:**Sum***From:*mjumbo <mjumbo@nm.ru>