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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: [mg31371] Re: Can NDSolve find the other solution???
  • From: "cosmicstring" <cosmicstring at yahoo.com>
  • Date: Wed, 31 Oct 2001 03:31:02 -0500 (EST)
  • References: <9rdgqi$7q0$1@smc.vnet.net> <9rlsjd$ncg$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Thank you...

I think my eq.s are stiff so I am trying some other ways with Mathematica
(Gear method of Mathematica failed but I have to do some other tests to my
program) and meanwhile I will be writing a Fortran code to solve the system.
I hope everything will be clearer soon...

Thank you again for your interest.


"Alois Steindl" <Alois.Steindl+e325 at tuwien.ac.at> wrote in message
news:9rlsjd$ncg$1 at smc.vnet.net...
> "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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