//#include <config.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_spline.h>
#include <gsl/gsl_interp.h>

static double fun(double x)
{
  return x + cos(x*x);
}

int main (void)
{
  const double a = 1.0;
  const double b = 10.0;
  const int steps = 10;
  double xi, yi, x[100], y[100], dx;
  FILE *input, *output;
  int i;

  input = fopen("wezly.txt","w");
  output = fopen("inter.txt","w");

  //przygotowanie danych
  {
  dx = (b - a) / (double) steps;
 
  for (i = 0; i <= steps; ++i) {
      x[i] = a + (double)i * dx + 0.5 * sin((double)3.14*i/steps); 
      y[i] = fun(x[i]);
      fprintf (input,"%g %g\n", x[i], y[i]);
  }
  }

  //interpolacja
  
  gsl_spline *spline 
    = gsl_spline_alloc (gsl_interp_polynomial, steps + 1);
  
  gsl_spline_init (spline, x, y, steps + 1);
  

  //probkowanie funkcji interpolacyjnej
  gsl_interp_accel *acc 
    = gsl_interp_accel_alloc ();
  
  for (xi = a; xi <= b; xi += 0.01) {
    yi = gsl_spline_eval (spline, xi, acc);
    fprintf (output,"%g %g\n", xi, yi);
  }
  
  gsl_spline_free (spline);
  gsl_interp_accel_free(acc);
  return 0;
}