using namespace RooFit;

void GaussPlot()
{
  RooRealVar x("x", "x", -10, 10);
  RooRealVar mean("mean", "mean of Gaussian", 0, -10, 10);
  RooRealVar sigma("sigma", "width of Gaussian", 3, -10, 10);

  RooGaussian gauss("gauss", "Gaussian PDF", x, mean, sigma);


  TCanvas * c1 = new TCanvas("c1", "Curva Gaussiana");
  TCanvas * c2 = new TCanvas("c2", "Hist Gaussiana");
  TCanvas * c3 = new TCanvas("c3", "Dati-Gaussiana");
	  
  c1-> cd();
  // Plot PDF
  RooPlot * xframe1 = x.frame(Title("Gaussian PDF"));
  gauss.plotOn(xframe1);
  xframe1-> Draw();
  
  //Generate a toy MC sample and Plot PDF
  RooDataSet * data = gauss.generate(x, 10000);

  c2-> cd();
  RooPlot * xframe2 = x.frame(Title("MC Gaussian data"));
  data-> plotOn (xframe2);
  xframe2->Draw();
  
  //ML fit of gauss to data

  c3-> cd();
  gauss.fitTo(*data);
  mean.Print();
  sigma.Print();

  RooPlot * xframe3 = x.frame(Title("ML Fit to a MC Gaussian sample"));
   data->plotOn(xframe3, Name("myHist1"));
   gauss.plotOn(xframe3, Name("myCurve1"));
   gauss.paramOn(xframe3);
   xframe3->Draw();


Double_t  chi2_1 = xframe3->chiSquare("myCurve1", "myHist1");
   cout<<"chi2 = " << chi2_1 << endl;

}