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}].
>