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MathGroup Archive 2005

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Re: Sum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55213] Re: Sum
  • From: Peter Pein <petsie at arcor.de>
  • Date: Thu, 17 Mar 2005 03:28:31 -0500 (EST)
  • References: <d192qe$ng4$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

mjumbo 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.
> 
Attributes@Sum
{HoldAll,Protected,ReadProtected}
 ^^^^^^^

so
x=Exp[-k];
Sum[Evaluate@x,{k,1,Infinity}]
will give what you want

-- 
Peter Pein
Berlin


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