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. > >

**References**:**Question for Partial differential summationseries***From:*dai <dahfsys@gmail.com>