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MathGroup Archive 2001

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Re: Can NDSolve find the other solution???

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31350] Re: Can NDSolve find the other solution???
  • From: Alois Steindl <Alois.Steindl+e325 at tuwien.ac.at>
  • Date: Tue, 30 Oct 2001 04:35:34 -0500 (EST)
  • Organization: Inst. f. Mechanics II, TU Vienna
  • References: <9rdgqi$7q0$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"cosmicstring" <cosmicstring at yahoo.com> writes:

> When I try NDSolve with those four first order ode's and four initial
> conditions I get only one solution but when I work the system out(without
> transforming to four 1st order eq.s) analytically I get two solutions which
> is trivial because I am solving 2nd order eq.s.
> 
Hello,
that's not trivial at all. I would bet that you made some serious
mistake. The first order system and the original system are
equivalent; any solution of one system is also a solution of the other
one.
And the solutions for well-behaved initial value problems are usually
unique, so you get the result you should.

Mathematica also allows you to use higher order equations, but that will not
help you with this problem.
You will have to re-think your equations and calculations.

> Now, I would like to know if there is a way to obtain the other solution
> using Mathematica. I need this solution because it is the physical one!
> 
The non-physical solution is very likely generated by mistakes in your
setup.

If you can't find your mistake, you could try to tell us your
equations and the solution you expect.

Alois
 


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