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MathGroup Archive 2001

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Re: NDSolve problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg31746] Re: NDSolve problem
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Sat, 1 Dec 2001 02:43:32 -0500 (EST)
  • Organization: Universitaet Leipzig
  • References: <9u4gqb$lpb$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

your system of equations has a singularity at this point
and one of the components goes to infinity. The stepsize 
control detect the singularity and reduce the stepsize
until it is to small.

You should care full analyse the differential equation
if the singularity is not expected/obvious.

With an ordinary differntial equations solver it is
impossible to jump over the singularity, because
the most ode solver use a polynomial approximation
to the solution and you can't approximate  1/x with 
a polynomial of positive powers. 

Regards
  Jens


deniz.seker at arcelik.com.tr wrote:
> 
> Hi,
> 
> I have a problem with NDSolve. I'm trying to solve 2 coupled differential
> equations. But dur,ng the solution, I saw a message that,"At t=.... step
> size is effect,vely zero, singularity suspected." Then, I'm trying to
> decrease StartingStepSize option up to 10^(-14) or increase MaxSteps to
> 100000. But, for these two cases, I couldn't get solutions for 6 hours run.
> What should I do?
> 
> Best regards,
> 
> Deniz
> 
> PS : If anybody wants to see the notebook, I can send via e-mail.


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