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MathGroup Archive 1999

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Question about evaluation with Sum

  • To: mathgroup at
  • Subject: [mg19587] Question about evaluation with Sum
  • From: CORNIL Jack Michel <jmcornil at>
  • Date: Sat, 4 Sep 1999 01:34:25 -0400
  • Sender: owner-wri-mathgroup at


I have a big problem of evaluation with the function Sum.

With the very simple following example, 


   Sum[p,{k, 1, n}]
     p k

   Sum[Evaluate[p], {k, 1, n}]
     - n (1+n)

   Sum[p,{k, 1, 5}]


how can I explain my students that 
   in the first case p is left unevaluate and it needs Evaluate,

   in the last case p is evaluate correctly  ?

I do not understand how the "Attributes" of Sum can explain this.

Thank You in advance

Jack Michel CORNIL

Versailles FRANCE

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