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Re: [Help-gsl] ODE solver gets stuck

From: Paul Schneider
Subject: Re: [Help-gsl] ODE solver gets stuck
Date: Wed, 16 Feb 2005 09:56:01 +0100
User-agent: Mozilla Thunderbird 1.0 (X11/20041227)

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.




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.



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