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MathGroup Archive 2005

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Re: Sum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg55221] Re: [mg55175] Sum
  • From: "David Park" <djmp at earthlink.net>
  • Date: Thu, 17 Mar 2005 03:28:41 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Why not use...

x = Exp[-k];
Sum[x // Evaluate, {k, 0, Infinity}]
E/(-1 + E)

or even better

f[k_] := Exp[-k]
Sum[f[k], {k, 0, Infinity}]
E/(-1 + E)					??

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/







From: mjumbo [mailto:mjumbo at nm.ru]
To: mathgroup at smc.vnet.net

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.
__________


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