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Re: Symbolic summation

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  • Subject: [mg101625] Re: Symbolic summation
  • From: Bill Rowe <readnews at>
  • Date: Fri, 10 Jul 2009 23:27:48 -0400 (EDT)

On 7/10/09 at 6:44 AM, Lucazanottifragonara at (Luca) wrote:

>The problem is that I want a solution of this form:


>Where the 1, 2, 3 and 4 and 5 are the summation subscripts...
>My summation is not infinite, I have to stop it.

>If I write something like this:

>n = 3;

>Sum[kl, {l, 2, n}]

>I obtain 2kl, instead I want to obtain k2+k3.

Mathematica sees the syntax above as saying the summand is a
variable named kl and the summation index is l. Since kl and l
are distinct and no relationship between them has been provided,
Mathematica returns the correct answer 2 kl. What you've
described can be done as follows:

In[2]:= Sum[Subscript[k, j], {j, 2, 3}]

Out[2]= Subscript[k, 2] + Subscript[k, 3]

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