KroneckerDelta in sum
- To: mathgroup at smc.vnet.net
- Subject: [mg31675] KroneckerDelta in sum
- From: Matthias Reichelt <reichelt at ax1348.physik.uni-marburg.de>
- Date: Fri, 23 Nov 2001 05:47:27 -0500 (EST)
- Organization: Uni Marburg
- Sender: owner-wri-mathgroup at wolfram.com
Hi all, I guess I have a rather simple problem. If I write Sum[a[i, j]KroneckerDelta[i - j], {i, -Infinity, Infinity}] Mathematica answers a[j, j] Now, if I use a two-fold sum Sum[a[i, j]KroneckerDelta[i - j], {i, -Infinity, Infinity}, {j, -Infinity, Infinity}] the expression is not simplified. How can I force Mathematica to give results like Sum[a[j,j],{j,-Infinity, Infinity}] Thks, Matthias Reichelt +--------------------------------------------------+ | Matthias Reichelt | | | Department of Physics | phone: +49-6421-28-24217 | | Philipps-University | | | Renthof 5 | fax: +49-6421-28-27076 | | 35032 Marburg | | | Germany | | +--------------------------------------------------+