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MathGroup Archive 1996

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Problem with discontinuity in NDSolve[]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4301] Problem with discontinuity in NDSolve[]
  • From: a_kowald at chemie.fu-berlin.de (Axel Kowald)
  • Date: Tue, 9 Jul 1996 00:46:47 -0400
  • Organization: Kristallographic Institute FU Berlin
  • Sender: owner-wri-mathgroup at wolfram.com

Hi everybody,

I have a problem with NDSolve if my equation contains a discontinuity.
If I try

NDSolve[{y'[t] == 10 - y[t] * If[y[t]-15 <= 0, 0, 1], 
         y[0] == 0}, y, {t,0,20}]

I always get the error:  Maximum number of steps reached.
The solution should be a linear increase until y = 15 followed by an 
exponential decay until a steady state is reached by y = 10


Funny enough if I try 

NDSolve[{y'[t] == 10 - y[t] * If[t-15 <= 0, 0, 1], 
         y[0] == 0}, y, {t,0,20}]


causing the discontinuity to be at t = 15 instead of y = 15 NDSolve has no
problems at all. (But of course this is not what I want.)


ANY SOLUTIONS ???     ANY IDEAS  ???



Many thanks


	Axel Kowald


P.S. I'm using Mma 2.2 on a Mac with 7.5.3 and 24 MB RAM


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