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Re: NDSolve with side conditions:

  • To: mathgroup at
  • Subject: [mg32755] Re: [mg32709] NDSolve with side conditions:
  • From: Reza Malek-Madani <mail at>
  • Date: Fri, 8 Feb 2002 03:49:29 -0500 (EST)
  • Reply-to: research at
  • Sender: owner-wri-mathgroup at

Have you tried this?

NDSolve[{y'[t]==f1[y[t], x[t], f3[y[t],x[t]]], 
         x'[t]==f2[y[t], x[t], f3[y[t],x[t]]], 
         y[0]==y0, x[0]==x0},
         {y, x}, {t,0, 100}] 


On Thu, 7 Feb 2002, Thomas Steger wrote:

> The following ordinary differential equation system is given:
> y'(t)=f1[y(t),x(t),z(t)]; x'(t)=f2[y(t),x(t),z(t)] and
> z(t)=f3[y(t),x(t)]. z(t) is given in implicite and integrated form.
> The question reads as follows: Can Mathematica solve this system
> numerically by NDSolve. I have tried the following syntax:
> NDSolve[{y'[t]==f1[y[t], x[t], z[t]], x'[t]==f2[y[t], x[t], z[t]],
> z(t)==f3[y[t], x[t]], y[0]==y0, x[0]==x0, z[0]==z0},{y[t], x[t],
> z[t]},{t, 0, 100}].
> I could differentiate z(t)=f3[y(t),x(t)] with respect to t; this would
> yield  a standard 3-dimensional DES. But I would like not to increase
> the dimension.
> Thanks for any help!

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