diff differentiates with respect to a single variable. c[t] is an infinite
set of variables within the sum, and t is a bound variable within the sum,
so it is not clear what differentiating the whole thing with respect to c[t]
should mean.
Compare the following simpler case: Suppose you had simply sum(c[t],t,0,1)
= c[0]+c[1]. What would you expect diff(c[0]+c[1],c[t]) to be?
If you want to differentiate within the summand for each c[t], try
substpart(diff(piece,c[t]),%o1,1);
On 8/14/06, J. Li <lij53 at univmail.cis.mcmaster.ca> wrote:
>
> Dear all,
>
> I have a question about taking differentiation within a summation
> expression. I defined the objective function as a summation of periodic
> functions and tried to take the differentiation of the objective
> function with respect to a variable in a specific period,
> c[t].
>
> objf: sum (A^t*(log(c[t])+B*log(1-n[t])), t, 0, inf);
> diff(objf, c[t]);
>
>
> It didn't take differentiation. I don't know why is this happening. Can
> I take differentiation within summation at all? Thanks for your help.
>
>
> Jinhu Li
>
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