No, u dont give up stepsize control. U just calculate until u have reached desired point, and then restart to the next point. About speed, rk8pd is quite fast, i use it for mhd problems. The manual is quite helpful & distilled about ODEs. It will help u.
> Dear Periklis, > > Thanks for your help! Maybe I didnot understand your method correctly. > Do you give up the adaptive step-size control in ODE45? I really like > the adaptive step-size error control scheme and in order to make sure > that my solution is within 1e-6 error I really need the automatic > step-size error control. > > Is there a way to still retain the adaptive step-size error control in > ODE45 but only output at t=5, 7, 9, 11 four time points? > > Any more thoughts on other speed-up improvements? > > Thanks a lot! > > > > On 6/6/07, Periklis Rammos <[EMAIL PROTECTED]> wrote: >> Hello, >> >> About your question >> > I want to solve the system of ODEs at 5, 7, 9, 11 seconds, and I >> > only want solutions at these points. How to do that? >> >> In GSL manual there is something i think directly addresses your >> problem: >> http://www.gnu.org/software/gsl/manual/html_node/ODE-Example-programs.html >> ------------------------------------------------------------------------ >> To obtain the values at regular intervals, rather than the variable >> spacings chosen by the control function, the main loop can be modified >> to >> advance the solution from one point to the next. For example, the >> following main loop prints the solution at the fixed points t = 0, 1, 2, >> \dots, 100, >> >> for (i = 1; i <= 100; i++) >> { >> double ti = i * t1 / 100.0; >> >> while (t < ti) >> { >> gsl_odeiv_evolve_apply (e, c, s, >> &sys, >> &t, ti, &h, >> y); >> } >> >> printf ("%.5e %.5e %.5e\n", t, y[0], y[1]); >> } >> -------------------------------------------------------------------------- >> >> Hope it helps :) >> >> >> >> ----------------------------------------------------------------------- >> Perikles Rammos >> Section of Astrophysics, Astronomy & Mechanics >> Department of Physics, University of Athens >> Panepistimiopolis, 157 84 Zografos >> Athens, GREECE >> Tel. 00 30 - 210 - 7276864 >> email: [EMAIL PROTECTED] >> ----------------------------------------------------------------------- >> >> >> >> _______________________________________________ >> Help-gsl mailing list >> [email protected] >> http://lists.gnu.org/mailman/listinfo/help-gsl >> > _______________________________________________ Help-gsl mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-gsl
