int
integrate_ode_using_driver (double t, double t1, double y[], int n_steps,
double h_init, double h_max, double eps_abs,
double eps_rel, void *params, int print_values)
{
int i; // Counter in macro-step loop
int j; // Counter in print loop
int status;
size_t dim = NY;
double ti;
double dt = (t1-t)/(double)n_steps;
const gsl_odeiv2_step_type * T = gsl_odeiv2_step_msbdf;
gsl_odeiv2_step * s = gsl_odeiv2_step_alloc (T, dim);
gsl_odeiv2_system sys = {func, jac, dim, params};
gsl_odeiv2_driver * d = gsl_odeiv2_driver_alloc_y_new(&sys, gsl_odeiv2_step_msbdf, h_init, eps_abs, eps_rel);
gsl_odeiv2_step_set_driver(s, d);
if (h_max > 0.0)
{
gsl_odeiv2_driver_set_hmax(d, h_max);
}
for (i = 0; i < n_steps; ++i)
{
// Macro-step loop
ti = t + dt*(i+1);
status = gsl_odeiv2_driver_apply (d, &t, ti, y);
if (status != GSL_SUCCESS)
{
printf ("error, return value=%d\n", status);
break;
}
if (print_values)
{
printf(STRINGIFY(PRECISION), t);
for (j = 0; j < NY; ++j)
{
printf(" " STRINGIFY(PRECISION), y[j]);
}
printf("\n");
}
}
gsl_odeiv2_driver_free (d);
gsl_odeiv2_step_free (s);
return status;
}
int
main () {
double alpha = 2;
double beta = 4;
double gamma = 7; //3 and 7
double gmax = 5;
// you can use any stepper here
const gsl_odeiv2_step_type * T = gsl_odeiv2_step_rk4imp;
gsl_odeiv2_step * s = gsl_odeiv2_step_alloc(T, 3);
gsl_odeiv2_control * c = gsl_odeiv2_control_y_new(1e-6, 0.0);
gsl_odeiv2_evolve * e = gsl_odeiv2_evolve_alloc(3);
predprey_params pars = {alpha,beta,gamma,gmax,0,0}; /* the parameters */
gsl_odeiv2_system sys = {predprey, jac_predprey, 3, &pars};
gsl_odeiv2_driver * d = gsl_odeiv2_driver_alloc_y_new(&sys, T, 1e-6, 1e-6, 1e-6 );
gsl_odeiv2_step_set_driver(s, d);
double t = 0.0, t1 = 20.0;
double h = 1e-6;
double x[3] = { 1.0, 0.1, 3.0 };
double t2 = t;
double interval = 0.01;
while (t < t1)
{
int status = gsl_odeiv2_evolve_apply (e, c, s, &sys, &t, t1, &h, x);
if (status != GSL_SUCCESS)
break;
if(t > t2+interval) {
printf ("%.5e %.5e %.5e %.5e\n", t, x[0], x[1], x[2]);
t2 = t;
}
}
gsl_odeiv2_evolve_free (e);
gsl_odeiv2_control_free (c);
gsl_odeiv2_step_free (s);
fprintf(stderr,"Number of Jacobian evaluations = %d\n"
"Number of Function evaluations = %d\n", pars.jac_count,
pars.count);
return 0;
}
gsl_odeiv2_driver *
gsl_odeiv2_driver_alloc_scaled_new (const gsl_odeiv2_system * sys,
const gsl_odeiv2_step_type * T,
const double hstart,
const double epsabs, const double epsrel,
const double a_y, const double a_dydt,
const double scale_abs[])
{
/* Initializes an ODE driver system with control object of type
scaled_new.
*/
gsl_odeiv2_driver *state = driver_alloc (sys, hstart, T);
if (state == NULL)
{
GSL_ERROR_NULL ("failed to allocate driver object", GSL_ENOMEM);
}
if (epsabs >= 0.0 && epsrel >= 0.0)
{
state->c = gsl_odeiv2_control_scaled_new (epsabs, epsrel, a_y, a_dydt,
scale_abs, sys->dimension);
if (state->c == NULL)
{
gsl_odeiv2_driver_free (state);
GSL_ERROR_NULL ("failed to allocate control object", GSL_ENOMEM);
}
}
else
{
gsl_odeiv2_driver_free (state);
GSL_ERROR_NULL ("epsabs and epsrel must be positive", GSL_EINVAL);
}
/* Distribute pointer to driver object */
gsl_odeiv2_step_set_driver (state->s, state);
gsl_odeiv2_evolve_set_driver (state->e, state);
gsl_odeiv2_control_set_driver (state->c, state);
return state;
}
