Derivative, Sum and KroneckerDelta symbolically
- To: mathgroup at smc.vnet.net
- Subject: [mg25040] Derivative, Sum and KroneckerDelta symbolically
- From: Stefan Eder <stefan.eder at eunet.at>
- Date: Fri, 1 Sep 2000 21:57:49 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
does anybody know how to tell Mathematica to solve
"Sum[D[Sum[x[n], {n, 1, k}], x[i]], {i, 1, k}]" correctly?
In my opinion the expression should give "k" as result, Mathematica says
"0".
Introducing concrete values instead of k the result is correct:
"Sum[D[Sum[x[n], {n, 1, 5}], x[i]], {i, 1, 5}]" = "5".
Is there a possibility to tell Mathematica that the expressions above
lead to a "KroneckerDelta":
Sum[KroneckerDelta[n, i], {n, 1, k}, {i, 1, k}]
Thanks,
Stefan