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Re: Question for Partial differential summationseries

  • To: mathgroup at smc.vnet.net
  • Subject: [mg122895] Re: Question for Partial differential summationseries
  • From: Ralph Dratman <ralph.dratman at gmail.com>
  • Date: Mon, 14 Nov 2011 07:09:28 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201111110952.EAA08411@smc.vnet.net>

When you take the derivative of a sum over i, there will have to be a
sum over i in the result. I think you have got the equation mixed up
somehow, maybe from lecture notes.  Looking at the big and small x and
X, y and Y, p and P, I think it is supposed to look something like
this:

X = Sum[Subscript[x, i][t], {i, 1, N}];
Y = Sum[Subscript[y, i][t], {i, 1, N}];
P = Sum[Subscript[p, i][x y], {i, 1, N}];
W = Y*P;
D[W, Y] == P;

True

Still not very meaningful, but least the answer is as proposed.

Ralph

On Fri, Nov 11, 2011 at 4:52 AM, dai <dahfsys at gmail.com> wrote:
> The function defined as follow
>
>
> x = X[t];
> y = Y[i, t];
> p = P[i, xv];
> w = Sum[y*p, {i, 1, N}];
>
> When we excuted partial differential "w" by "y"
> the exact solution is "p" (or P[i, xv]).
>
> However, the solution in Mathematica package is
> Sum[p, {i, 1, N}].
>
> How can I obtain the correct solution? please help.
>
>



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