Re: [Help-gsl] ODE solver gets stuck

[Paul Schneider]

Paul Schneider wrote:

> I'm trying to solve a system of ODE's with GSL. I have to say that I 
> have no experience with ODE's and especially not with numerically 
> nolving them. Therefore please don't hold back even with very basic 
> hints.
>
> My problem: a 4 dimensional ODE can be solved rapidly, only for some 
> parameter constellations GSL seems to get stuck in some loop and I 
> have to manually kill the program. I looked at the output during such 
> an incident and it seems that at some point t from below doesn't 
> increase anymore, but the function values grow infinitely. I have 
> tried all the solvers, with and without Jacobian. The following code 
> is what I think is the relevant portion of my C++ program using GSL. 
> TinyVector (PVec) is from the Blitz library.
>
> The function odeSolve below is called thousands of times for different 
> (global) parameters KQd_ThQd_, KQd_. I am very grateful to all hints 
> how I can get this to work. The ODE itself has not been reported to be 
> especially difficult to handle.
>
> Thanks,
>
> Paul
[snip]

I tried the same problem with matlab. Same thing. It doesn't seem to be 
GSL related. The only difference is that matlab doesn't get stuck, but 
returns with a message that it would have to choose a step size below 
the minimum step size 5.5e-15.

Can anybody give me a hint how I could tweak GSL to give me a solution. 
Or are the ODE's just not solvable for certain parametrizations? AS 
mentioned above, I am a beginner.

Thanks,

Paul