void integrate_landau()
{
  double xmin=-3.;
  double xmax=35.;
  TF1* func = new TF1("landau","landau",xmin,xmax);
  func->SetParameters(1., 0., 1.);
  func->Draw();

  fstream f1;
  f1.open("data/landau_integral.txt",ios::out);

  double middle = 1.35645; // not mathematically sound...

  int nbins=300000;
  for (int i=0; i<nbins; i++){
    double x = xmin+(double)i*(xmax-xmin)/(double)nbins;
    double out1 = func->Integral(xmin,x);
    double out2 = func->Integral(middle,x);
    cout << "x = "<< x << ", out1 = " << out1  << ", out2 = " << out2 << endl;
    f1 << x << " " << out1 << " " << out2 << endl;
  }
  f1.close();

}