#include <stdlib.h>

#include <stdio.h>

#include <math.h>

#include <gsl/gsl_errno.h>

#include <gsl/gsl_spline.h>

int

main (void)

{

  int N = 4;

  double x[4] = {0.00, 0.10,  0.27,  0.30};

  double y[4] = {0.15, 0.70, -0.10,  0.15}; 

             /* Note: y[0] == y[3] for periodic data */

  gsl_interp_accel *acc = gsl_interp_accel_alloc ();

  const gsl_interp_type *t = gsl_interp_cspline_periodic; 

  gsl_spline *spline = gsl_spline_alloc (t, N);

  int i; double xi, yi;

  printf ("#m=0,S=5\n");

  for (i = 0; i < N; i++)

    {

      printf ("%g %g\n", x[i], y[i]);

    }

  printf ("#m=1,S=0\n");

  gsl_spline_init (spline, x, y, N);

  for (i = 0; i <= 100; i++)

    {

      xi = (1 - i / 100.0) * x[0] + (i / 100.0) * x[N-1];

      yi = gsl_spline_eval (spline, xi, acc);

      printf ("%g %g\n", xi, yi);

    }

  gsl_spline_free (spline);

  gsl_interp_accel_free (acc);

  return 0;

}