> objf: sum (A^t*(log(c[t])+B*log(1-n[t])), t, 0,
> inf);
> diff(objf, c[t]);
You didn't put any variable in your formula; there is
only the descrete variable t, and you are summing over
t, so t vanishes. I mean:
the expression sum_{t} f(t,x) is a function of the
(continous) variable x, and you can try to
differentiate it. But the expression sum_{t} f(t), and
this was your case, is just a number, if the sum
converges. So if the sum converges, the derivative is
zero, otherwise differentiate it has no sense.
But maybe I don't understand the maxima syntax: I
interpreted n[t] and c[t] as functions of the
descrete variable t. Was I wrong?
Giovanni Gherdovich
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