using namespace RooFit ;

void ex15()
{
  gSystem->Load("libRooFit") ;

  TFile* f = TFile::Open("ex15.root") ;
  TH1* h_sig = f->Get("h_sig") ;
  TH1* h_bkg = f->Get("h_bkg") ;
  TH1* h_data = f->Get("h_data") ;
  TH1* h_data_small = f->Get("h_data_small") ;
  TH1* h_data_large = f->Get("h_data_large") ;
  
  // Create a workspace with observable x[0,120]
  RooWorkspace w("w",1) ;
  w.factory("x[20,120]") ;
  w->var("x")->setBins(20) ;
  
  // Tie TF1 h_sig to observable x in RooFit binned dataset dh_sig
  RooDataHist dh_sig("dh_sig","dh_sig",*w.var("x"),h_sig) ;

  // Same for the other datasets
  RooDataHist dh_bkg("dh_bkg","dh_bkg",*w.var("x"),h_bkg) ;
  RooDataHist data("data","data",*w.var("x"),h_data) ;
  RooDataHist data_small("data_small","data_small",*w.var("x"),h_data_small) ;
  RooDataHist data_large("data_large","data_large",*w.var("x"),h_data_large) ;

  // Import both template datasets in the workspace
  w.import(dh_sig) ;
  w.import(dh_bkg) ;

  // Construct yield functions, as done in Ex 10
  w.factory("HistFunc::hf_sig(x,dh_sig)") ;
  w.factory("HistFunc::hf_bkg(x,dh_bkg)") ;

  // In ex10 we used 100 bins, now we use 20, which causes the
  // bin width to change from 1 unit of x to 5 units of x.
  //
  // This modifies the expected yields with that factor
  // To keep the original interpretation of the mu and nu
  // parameters of ex 10, we multiply these with the
  // inverse of the bin width, i.e. 0.2  
  w.factory("prod::ksig(mu[1,0,5],binw[0.2])") ;
  w.factory("prod::kbkg(nu[1],binw)") ;

  // Construct a probability model from the sum of two yield functions
  w.factory("ASUM::model(ksig*hf_sig,kbkg*hf_bkg)") ;

  w.Print("t") ;
  
}