#include <gsl/gsl_interp.h>
#include <gsl/gsl_spline.h>
double chi(double cotpsi);
int init(double rmax, double rela_err_limit, int *size, double **x, double **y);

typedef struct {
  gsl_spline *spline;
  gsl_interp_accel *acc;
} Spline_data ;