Re: partial derivative of a sum
- To: mathgroup at smc.vnet.net
- Subject: [mg59806] Re: [mg59788] partial derivative of a sum
- From: Pratik Desai <pdesai1 at umbc.edu>
- Date: Mon, 22 Aug 2005 02:48:23 -0400 (EDT)
- References: <200508210751.DAA26559@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Daniel Roy wrote: >I'm wondering if Mathematica can handle expressions such as: > > ClearAll[n, l] > D[Sum[n[i] l[i], {i, 1, Infinity}], n[10]] > >The answer should be l[10], but Mathematica returns 0. > > ClearAll[n, l] > D[Sum[n[i]l[i], {i, 1, 100}], n[10]] > >return l[10] as expected. More generally, > > ClearAll[n, l] > Assumptions[N \[Element] Integers && N>10, > D[Sum[n[i] l[i],{i,1,N}], n[10]] > >Thanks, >Dan Roy > > > Here is my attempt using Subscript and Total ClearAll[n, l, i, m] m = 100000 n[i_] = Table[Subscript[n, i], {i, 1, m, 1}]; l[i_] = Table[Subscript[l, i], {i, 1, m, 1}]; D[n[i]*l[i] // Total, Subscript[n, 10]] Hope this helps Pratik -- Pratik Desai Graduate Student UMBC Department of Mechanical Engineering Phone: 410 455 8134
- References:
- partial derivative of a sum
- From: Daniel Roy <droy@mit.edu>
- partial derivative of a sum