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Taking the derivative of a summation
*To*: mathgroup at smc.vnet.net
*Subject*: [mg95820] Taking the derivative of a summation
*From*: Alberto Lioy <nonalignmentpact at yahoo.it>
*Date*: Wed, 28 Jan 2009 06:29:26 -0500 (EST)
Hi everybody, I am an italian student in economics who is trying to solve an utility maximization problem (in Blanchard-Kiyotaki model)...I'm actually in trouble because I cannot have mathematica 5 take the derivative of a symbolic summation...
the case is the one of a summation of c(i)*p(i) with i between 1 and k
I want to take the derivative for a generic element c(i) (p(i) is taken as fixed)
.now if I do D[Sum[Subscript[C,i]*Subscript[P, i], {i, 1, k}, Subscript[c, i]]
the program answers with Sum[Subscript[P, i], {i, 1, k}]
which is the summation of the p(i) elements...
I think that mathematica did not understand that I wanted to take the derivative for A generic element and gave me instead the derivative for EACH element..
I tried to take the dervative of c(1), c(k) or whatever...and it answers 0 (as was expectable)
the result I'm trying to obtain is p(i)...
maybe I just don't use the right commands...could anybody give me a piece of advice? thank you in any case
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