Re: [Help-gsl] problem

[Pau Cervera Badia]

gsl_odeiv_evolve_apply(e,c,s,&sys,&t,t1,&h,y) will advance from time t 
to the next integration time with an optimum step-size, provided that 
the next time is less than t1. Otherwise it will integrate the system to 
t1 exactly. So after some iterations the while condition will be false.

You can check that gsl_odeiv_evolve_apply is running properly with:

while (t < t1) {

   int status = gsl_odeiv_evolve_apply(e,c,s,&sys,&t,t1,&h,y);

   printf("%.5e %.5e\n", t, t1); // this should print t less than t1

   if (status != GSL_SUCCESS)
      break;

}
printf("%.5e %.5e\n",t,t1); // this should print t equal to t1

If I'm not missing something, your program should work. Maybe the 
problem is that t is always less than t1 for some other reason (maybe 
the routine couldn't reach the prescribed precision and 
gsl_odeiv_evolve_apply is trying to reduce the step-size more and more). 
Maybe you can check the h values.

Maybe something will be of any help.

address@hidden wrote:

> Hi:
>
> I use ordinary differential equations from GSL. The part of my program is like 
> example shown in the document.
>
>  const gsl_odeiv_step_type * T 
>    = gsl_odeiv_step_rk8pd;
>
>  gsl_odeiv_step * s 
>    = gsl_odeiv_step_alloc (T, 9);
>  gsl_odeiv_control * c 
>    = gsl_odeiv_control_y_new (1e-6, 0.0);
>  gsl_odeiv_evolve * e 
>    = gsl_odeiv_evolve_alloc (9);
>
>  double mu = 10;
>  gsl_odeiv_system sys = {func, NULL, 9, &mu};
>
>  double t = 0.0;  
>  double h = 1e-6;
>
>  for (i = 1; i <no_of_data_points; i++) {
>     t1 = mytable[i];
>     while (t < t1)
>     {
>        int status = gsl_odeiv_evolve_apply (e, c, s,
>                                           &sys, 
>                                           &t, t1,
>                                           &h, y);
>
>      if (status != GSL_SUCCESS)
>          break;
>      }
>      ...
>   }
>  gsl_odeiv_evolve_free (e);
>  gsl_odeiv_control_free (c);
>  gsl_odeiv_step_free (s);
>
> The weird thing is that at some i, the program stuck inside of "while" loop and 
> never come out. gsl_odeiv_evolve_apply will give t=t, so t is always < t1. As 
> result the program never stop. Dose anyone know how to solve this problem? 
> Thanks.
>
> Jun Cao
>
>
>
> _______________________________________________
> Help-gsl mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/help-gsl
>
>
>  

--
Pau Cervera i Badia (e-mail address@hidden)
{
  Departament de Física Fonamental                 Martí i Franqués, 1
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