Re: [Help-gsl] rk4

[Brian Gough]

At Thu, 3 Jan 2008 11:41:20 +0100,
Jochen Küpper wrote:
> Dear Brian,
> 
> have you ever been able to resolve this issue?
> 
> On 26.06.2007, at 20:28, Brian Powell wrote:
> 
> > This email is in reference to what appears to be a notable change in  
> > performance of the rk4 integrator between older and newer versions  
> > of gsl. In particular, rk4 from version 1.5 and version 1.8.  The  
> > particular test that I am performing is I am integrating a system of  
> > ODE's from some initial point to some final point, then reversing  
> > the integration.  Clearly, one expects such evolutions to overlap.   
> > Surprisingly, they overlap quite well with the older version of rk4,  
> > but they do not match up well at all with the newer version.  I'm  
> > trying to track down the cause of this, and, so far, can't seem to  
> > find a system specific reason for this.

I heard back that the explanation in 
http://lists.gnu.org/archive/html/bug-gsl/2007-07/msg00001.html
solved the problem.

-- 
Brian Gough

At Tue, 3 Jul 2007 17:48:47 -0400 (EDT),
Brian Powell wrote:
> 
> Brian,
> 
> > If you use a stricter tolerance do you still see the same problem of
> > the forward and backward evolution not matching up?
> 
> Yes, the solutions match up much better now.  Thank you very much for your
> quick reply.
> 
> Brian
>