Re: [Help-gsl] ODE solvers and overdamped motion

[Tuomo Keskitalo]

Hello,

On Fri, Sep 11, 2009 at 11:57 AM, Jonny Taylor <address@hidden> wrote:

> My problem involves a multi-particle system, with complicated inter-particle
> forces, but the issue I am having can be seen in a simple overdamped spring
> calculation (the derivatives function simply returns dydt[i] = -y[i] * 9.0).

How large a value i is? Hopefully not too large.

> I use the RK45 stepper, and error control gsl_odeiv_control_y_new(1e-2, 0).

I think you really should use relative tolerance as well. Also, you
probably want to try tighter tolerances, like 1e-6 or 1e-8 for both.
You can try to compare the resulting y with different abstol and
reltol to see what is "tight enough". I suggest bsimp as the stepper
if your problem is stiff.

-- 
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