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DiscreteDelta and RSolve Bug?

• To: mathgroup at smc.vnet.net
• Subject: [mg67981] DiscreteDelta and RSolve Bug?
• From: "Mariusz Jankowski" <mjankowski at usm.maine.edu>
• Date: Thu, 20 Jul 2006 06:04:14 -0400 (EDT)
• Organization: University of Southern Maine
• Sender: owner-wri-mathgroup at wolfram.com

Hello, I recently came across the following situation while solving a
difference equation, specifically the unit impulse response of a simple
system. For this example I have reduced the system to a first-order as it
illustrates the main problem.

The following evaluation seems to hang

RSolve[{y[n] - 1/2 y[n - 1] == DiscreteDelta[n], y[-1] == 0}, y[n], n]



Is there an explanation? Note that the following alternatives work as
expected: 

RSolve[{y[n] - 1/2 y[n - 1] == 0, y[0] == 1}, y[n], n]

RSolve[{y[n] - 1/2 y[n - 1] == KroneckerDelta[n], y[-1] == 0}, y[n], n]





Thanks, Mariusz

• Follow-Ups:
  • Re: DiscreteDelta and RSolve Bug?
    • From: Devendra Kapadia <dkapadia@wolfram.com>