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Re: Solving a Sum

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  • Subject: [mg89885] Re: Solving a Sum
  • From: magma <maderri2 at>
  • Date: Tue, 24 Jun 2008 03:20:43 -0400 (EDT)
  • References: <g3nhb2$g0$>

On Jun 23, 8:54 am, Igor <pisc... at> wrote:
> Hi All!
> I just started using mathematica for university and encounter the following issue which I am not able to figure out myself.
> I have to equations:
> eq1:=Sum[(Subscript[z,t]+Subscript[c,t]*Subscript[c,0])*q^(-t),{t,1,T}]==Subscript[z,0]+Sum[Subscript[z,t]*q^(-t),{t,1,T}]
> and
> eq2:=Subscript[z,t]==Subscript[s,t]*u
> I would like to solve these equations for c_t but get the following error message when using the Solve command as follows:
> Solve[{eq1, eq2}, C]
> Solve::tdep: The equations appear to involve the variables to be solved for in an essentially non-algebraic way. >>
> How can I solve this problem?
> Thanks a lot!
> Igor

Mathematica does not handle quantities with subscripts too well.
So when I have fixed subscripts I just use a variable like z0 or c1
and only at the end I make the substitution

z0-> Subscript[z,0]
for example, to get a nice printing.

in your case however, the subscripts are variables over the integers,
so you should represent the subscripted variables as z[t] and c[t],
that is as functions of t.
Even if you do this however, Mathematica will not solve your problem, because
you have a symbolic sum (how much is T?)

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