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Re: NDSolve with Piecewise function

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  • Subject: [mg87905] Re: NDSolve with Piecewise function
  • From: Albert Retey <awnl at>
  • Date: Sat, 19 Apr 2008 23:50:30 -0400 (EDT)
  • References: <fuc7ut$a30$>

Adam Simpson wrote:
> Hi, I am wanting to use NDSolve on a piecewise function but am running  
> into some trouble. Basically what I want to do is this:
> NDSolve[
> {Piecewise[{{FunctionsA, -.001 < x < .001}}, FunctionsB]}
> , {x, y, z}, {t,10^-5}]
> So I have x,y,z as functions of t that I want to solve for and in a  
> certain region of x I want to use a different set of equations. I am  
> not really sure if I can go about it this way or not though. Any help  
> on how to tackle such an equation would be greatly appreciated.
Basically it should work as intended, but remember that you need to give 
arguments to x,y,z in all your equations. The following works:

   x'[t] == Piecewise[{{Sin[x[t] + y[t]], y[t] > 0.2}}],
   y'[t] == Cos[x[t] + y[t]], x[0] == 0, y[0] == 0
   }, {x, y}, {t, 0, 1}



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