Re: [Help-gsl] questions about using GSL's ODE solver?

[Michael]

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 <address@hidden> 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: address@hidden
> -----------------------------------------------------------------------
>
>
>
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