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MathGroup Archive 2005

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Re: Sum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55231] Re: [mg55175] Sum
  • From: DrBob <drbob at bigfoot.com>
  • Date: Thu, 17 Mar 2005 03:29:03 -0500 (EST)
  • References: <200503161035.FAA23742@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

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


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