void draw(){



   Double_t masses[3] = { 3.686, 0.139, 0.139} ;


  double x_min = (masses[0]+masses[1])*(masses[0]+masses[1]);
  double x_max = (4.4-masses[1])*(4.4-masses[1]); // the range change from 4.42 to 4,2;
   RooRealVar  x("X1", "Y1", x_min, x_max);
   RooRealVar  y("X2", "Y2", x_min, x_max);

   TFile *f_phsppi0pi0 = new TFile("toymc.root");

   TH2F *h2 = (TH2F*)f_phsppi0pi0->Get("h2");

   RooDataHist sig2d_hist("sig2d_hist",      "sig2d_hist",  RooArgSet(x,y),        h2);
   RooHistPdf  sig2d_shape("sig2d_shape",     "sig2d_shape",      RooArgSet(x,y),        sig2d_hist , 1);

   RooDataSet* data2 = sig2d_shape.generate(RooArgSet(x,y),1000000);

   TH2F * hist=data2->createHistogram(x,y,200,200);
   hist->Draw();


}