Integrator::Integrator() {
// Constructor
// Set the number of elements to be integrated
numelements = 4;
// Integration method as supplied by GSL
const gsl_odeiv2_step_type *Type = gsl_odeiv2_step_rk8pd;
//const gsl_odeiv2_step_type *Type = gsl_odeiv2_step_rkf45;
// Initialize GSL
step = gsl_odeiv2_step_alloc(Type, numelements);
control = gsl_odeiv2_control_yp_new(0, 1.0e-8); // absolute error, relative error
evolve = gsl_odeiv2_evolve_alloc(numelements);
// Set the initial stepsize to be quite small, in order to get good data on derivatives at the beginning
stepsize = minstepsize();
}
gsl_odeiv2_driver *
gsl_odeiv2_driver_alloc_yp_new (const gsl_odeiv2_system * sys,
const gsl_odeiv2_step_type * T,
const double hstart,
const double epsabs, const double epsrel)
{
/* Initializes an ODE driver system with control object of type yp_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_yp_new (epsabs, epsrel);
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;
}