Re: Solving a Sum

*To*: mathgroup at smc.vnet.net*Subject*: [mg89885] Re: Solving a Sum*From*: magma <maderri2 at gmail.com>*Date*: Tue, 24 Jun 2008 03:20:43 -0400 (EDT)*References*: <g3nhb2$g0$1@smc.vnet.net>

On Jun 23, 8:54 am, Igor <pisc... at gmx.net> 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?)