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Problem with Sum

• To: mathgroup at smc.vnet.net
• Subject: [mg44004] Problem with Sum
• From: Mariusz Jankowski<mjankowski at usm.maine.edu>
• Date: Fri, 17 Oct 2003 05:14:29 -0400 (EDT)
• Organization: University of Maine System testbed server
• Sender: owner-wri-mathgroup at wolfram.com

Hello, can someone explain the following result:

Sum[(-1)^m * (DiscreteDelta[1 - 2*m] - 2*DiscreteDelta[1 + 3*m]), {m, -Infinity, Infinity}]

gives I + 2 (-1)^(2/3)

Shouldn't the sum evaluate to zero, since for any value of m the summand is identically zero. Note that

Sum[(-1)^m * (DiscreteDelta[1 - 2*m] - 2*DiscreteDelta[1 + 3*m]), {m, -10, 10}] returns 0, as expected.

This looks like a bug, is it?

Thanks, Mariusz