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Re: Solving a Sum

  • To: mathgroup at smc.vnet.net
  • Subject: [mg89939] Re: Solving a Sum
  • From: Igor <pischek at gmx.net>
  • Date: Wed, 25 Jun 2008 06:23:24 -0400 (EDT)

Hi!

Thanks for your explanatory words.

However, I figured out that there are infinite solutions as the equations can be transformed to:

Sum[Subscript[c,t]*q^(-t),{t,1,T}]=1

In order to hold, Subscript[c,t] can for example equal Subscript[s,t]/Sum[Subscript[s,t]*q^(-t),{t,1,T}]

But as this shows, the problem as infinite solutions for differing variables Subscript[s,t]. However, if I enter this in Mathematica, the expressions are not simplified to 1 using variables. Only when substituting values in the following expression 

Sum[Times[Power[q,Times[-1,t]],Subscript[s,t],Power[Sum[Times[Power[q,Times[-1,t]],Subscript[s,t]],List[s,1,T]],-1]],List[t,1,T]]

is evaluated to 1.

Why is that so.

By the way. This is not some homework for university. Just trying to understand how to work with Mathematica because im interested in it. The solution for the problem is in the script and we are not even supposed to solve this on our own (because for students of business administration this is probably not decisive skill :) )


Best regards,
Igor


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