#define N 3

double Lagrange(double y, double ∗f, 
		double ∗x, int n);

int main()
{
  double x[N]={0.1, 1.3, 3.7};
  double f[N]={1.3, 2.4, 1.7};

  int Nstep=100;
  double stepSize=(4.0-x[0])/Nstep;
  int i;
  double xatt=x[0];
  for(i=0; i<Nstep; i++)
    {
      double v=Lagrange(xatt,f,x,N);
      //      print ( xatt, v);
      //brew
      //brew install gnuplot
      xatt+=stepSize;
    }

}