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Re: Derivative of a sum.

  • To: mathgroup at
  • Subject: [mg101632] Re: [mg101615] Derivative of a sum.
  • From: Bob Hanlon <hanlonr at>
  • Date: Sun, 12 Jul 2009 05:48:35 -0400 (EDT)
  • Reply-to: hanlonr at

Presumably you meant the sum to be

f[x_, n_] = E^(-x)*Sum[x^i/i!, {i, 0, n}]

Gamma[n + 1, x]/n!

fp[x_, n_] = D[f[x, n], x]


   Tooltip[f[x, n], "f"],
   Tooltip[fp[x, n], "fp"]},
  {x, 0, 5},
  PlotRange -> {-1, 1}],
 {n, 0, 4, Appearance -> "Labeled"}]

Bob Hanlon

---- Muntoni Giampaolo <muntoni.giampa at> wrote: 

In order to resolve a problem I have found the question of derivating  the 
expression e^(-x)*Sum(in i)(x^n/n!, (i,0,n));the solution is easy and is 
But using language of Mathematica I have obteined a different result with a 
ricorse of Gamma function...also recurring to the option of manipulate, 
changing the value of  integer n.
I would want to obtain the exact result with language of Mathematica and 
Manipulate respect to n and also plotting the original function and its 
derivative.(with manipulate)
Thanks for aids

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