using namespace RooFit;

void GaussGauss()
{
  TFile * f = new TFile("signal.root", "Read");
  TTree * t = (TTree*)f -> Get("signal");
  TCanvas * c1 = new TCanvas("c1", "c1", 1);
  
  c1->SetLogy();
  t->Draw("var1");

  RooRealVar var1("var1","var1",5.24,5.29);
  
  //DICHIARO IL DATASET
  RooDataSet data("data","data", t, RooArgSet(var1));




  RooRealVar mean1("mean1", "mean of fist Gaussian", 5.275, 5.270, 5.290);
  RooRealVar sigma1("sigma1", "width of first Gaussian", 0.001, 0, 2);
  RooGaussian gauss1("gauss", "First Gaussian PDF", var1, mean1, sigma1);
  
  RooRealVar mean2("mean2", "mean of 2nd Gaussian", 5.275, 5.260, 5.290);
  RooRealVar sigma2("sigma2", "width of 2nd Gaussian", 0.00001, 0, 2);
  RooGaussian gauss2("gauss2", "2nd Gaussian PDF", var1, mean2, sigma2);
  
  RooRealVar fraction("fraction", "fraction", 0.2, 0.0, 1.0);
  RooAddPdf * sum = new RooAddPdf("sum", "Total sig PDF", RooArgList(gauss1,gauss2), RooArgList(fraction));
  sum->fitTo(data, Minos(kFALSE));


  c1->cd();
  
  RooPlot * var1frame = var1.frame(Title("MC var1  signal  data"));
  data.plotOn (var1frame,  Name("Hist"));
  sum->plotOn(var1frame, Name("Fitpdf"));
  sum->plotOn(var1frame,Components(gauss1), LineStyle(kDashed));
  sum->plotOn(var1frame, Components(gauss2), LineStyle(kDotted));
  sum->paramOn(var1frame); 
  var1frame->Draw();

  Double_t  chi2 = var1frame->chiSquare("Fitpdf", "Hist");
  cout<<"chi2 = " << chi2 << endl;
}