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MathGroup Archive 1999

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Re: Some problems with DSolve and NDSolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19836] Re: Some problems with DSolve and NDSolve
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sun, 19 Sep 1999 01:20:23 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,


> 
> The problem is that NDSolve can handle only explicit systems of differential
> equations, i.e. ODE's of the form
> 
>   (x1', x2', ..., xn') == f(x1, x2, ..., xn),
> 
> but your equations are given in implicit form:
> 
>   f(x1, x2, ..., xn, x1', x2', ..., xn') == 0


That is simply not true. NDSolve can handle implicit equations as long
as the coefficient matrix is not singular. But *this* is exact the case
here.

Replace *one* of the i1'[t]-i2'[t] terms in the equations by
i1'[t]+i2'[t]
(the quations are still implicit) but now Solve[_,{i1'[t],i2't]}] can
transform
it to the explicit form.

Regards
  Jens


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