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MathGroup Archive 2003

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Re: Can someone tell me why NDsolve isn't working here?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg44051] Re: Can someone tell me why NDsolve isn't working here?
  • From: Alois Steindl <Alois.Steindl+e325 at tuwien.ac.at>
  • Date: Sun, 19 Oct 2003 01:10:52 -0400 (EDT)
  • References: <bmqplo$rhb$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Mizrandir schrieb:
> Hello, Im trying to solve a system of 6 differential equations with
> NDSolve but I can't get Mathematica to do it. I wrote:
> 
> R = 1;
> M = 1;
> L = 1;
> NDSolve[{Rx[t] + Fx[t] == 2M x''[t], Ry[t] + Fy[t] == 0, 
                                        ^^^^^^^^^^^^^^^^^^^
This isn't a differential equation. Why do you think it is one?

>     Fx[t] R == -M R x''[t], -Rx[t] == 
       ^ That starts a second equation for x''. Are you sure?
 >[...]

> And Mathematica gave me the following error:
> 
> NDSolve::"ndode": "Input is not an ordinary differential equation."
> 
I agree.

> Does anybody know what am I doing wrong. Can I use Mathematica to
> solve this?
> 
I have heard rumours that Mathematica 5.0 should be able to traet 
Differental-Algebraic equations.
Alois


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