Hi,
On 11/06/2013 05:25 PM, Rhys Ulerich wrote:
> full-order accuracy to be achieved. However, between RK4 steps one is
> permitted to change the parameters however one likes.
>
> Along that line of reasoning, I would expect
> gsl_odeiv2_evolve_apply (e, c, s, &sys, &t, t+1, &h, y);
> // modify system parameters in some fashion
> gsl_odeiv2_evolve_apply (e, c, s, &sys, &t, t+1, &h, y);
> to behave identically pre- and post-4771 as line 1 completes some
> number of full steps of the chosen scheme. That is, the modification
> in line 2 is not done in between substeps.
..
> Tuomo, is this use case supported and, if so, does 4771 break it in
> some fashion?
Indeed, it is not supported directly like that. You must call
evolve_reset (or driver_reset) in between to let the evolve system know
that your ODE system has been changed:
gsl_odeiv2_evolve_apply (e, c, s, &sys, &t, t+1, &h, y);
// modify system parameters in some fashion
gsl_odeiv2_evolve_reset (e);
gsl_odeiv2_evolve_apply (e, c, s, &sys, &t, t+1, &h, y);
Adding evolve_reset to Alan's case did speed it up magnificently, so I
think this was the culprit.
Reading the manual, I see that the need to call reset function is not
explicitly stated in this kind of a situation. I will add it to the manual.
Thanks for your bug report!
--
tuomo.keskit...@iki.fi
http://iki.fi/tuomo.keskitalo
