Hi all I'm in the process of coding an adaptive step-size Runge-Kutta method in C to solve some equations related to my research, but I'm seriously considering switching to GSL to avoid reinventing the wheel (and because my code is far from optimal). My main issue at the moment, looking at the example at https://www.gnu.org/software/gsl/manual/html_node/ODE-Example-programs.html, is that I am not sure how to adapt this to integrate BACK from an initial value. I.e, for a 2 dim. 1st order system with initial values given at a point away from the origin (on the positive real axis), how do I get the solver to take negative steps BACK to the origin? I would appreciate some help with this, an illustration in terms of the example would be perfect (or a nudge in the right direction). As far as I can determine I need to modify the call to the evolution routine in some way, but I find the documentation difficult to follow.
Regards Martin
