Re: Re: Sum

*To*: mathgroup at smc.vnet.net*Subject*: [mg55279] Re: [mg55232] Re: [mg55175] Sum*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Fri, 18 Mar 2005 05:33:55 -0500 (EST)*References*: <200503161035.FAA23742@smc.vnet.net> <opsnqm72iyiz9bcq@monster.ma.dl.cox.net> <200503170829.DAA21735@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

*This message was transferred with a trial version of CommuniGate(tm) Pro* For example: i = 3; Sum[1/i^2, {i, 1, Infinity}] Pi^2/6 while Sum[Evaluate[1/i^2], {i, 1, Infinity}] Infinity Andrzej Kozlowski On 17 Mar 2005, at 09:29, DrBob wrote: >>> 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 > >