void demo()
{
  RooWorkspace w("w",1) ;
  w.factory("SUM::genmodel(1000*Gaussian::g(x[-10,10],mg[0],3),1000*Uniform::u(x))") ;
  w::x.setBins(10) ;
  
  // The 'observed' data
  RooDataSet* obsData = w::genmodel.generate(w::x,AllBinned(),NumEvents(2000)) ;  

  // Make HistFuncs for sigma and background to serve as templates
  RooDataHist* dh_bkg = w::u.generateBinned(w::x,1000) ;
  RooDataHist* dh_sig = w::g.generateBinned(w::x,1000) ;

  RooRealVar Asig("Asig","Asig",1,0.01,10) ;
  RooRealVar Abkg("Abkg","Abkg",1,0.01,10) ;

  // ***** Case 0 - 'Rigid templates' *****

  // Construct histogram shapes for signal and background
  RooHistFunc p_h_sig("p_h_sig","p_h_sig",w::x,*dh_sig) ;
  RooHistFunc p_h_bkg("p_h_bkg","p_h_bkg",w::x,*dh_bkg) ;  

  // Construct the sum of these
  RooRealSumPdf model0("model0","model0",RooArgList(p_h_sig,p_h_bkg),RooArgList(Asig,Abkg),kTRUE) ;

  // ***** Case 1 - 'Beeston Barlow' *****

  // Construct parameterized histogram shapes for signal and background
  RooParamHistFunc p_ph_sig("p_ph_sig","p_ph_sig",*dh_sig) ;
  RooParamHistFunc p_ph_bkg("p_ph_bkg","p_ph_bkg",*dh_bkg) ;  

  // Construct the sum of these
  RooRealSumPdf model_tmp("sp_ph","sp_ph",RooArgList(p_ph_sig,p_ph_bkg),RooArgList(Asig,Abkg),kTRUE) ;

  // Construct the subsidiary poisson measurements constraining the histogram parameters
  RooHistConstraint hc_sig("hc_sig","hc_sig",p_ph_sig) ;
  RooHistConstraint hc_bkg("hc_bkg","hc_bkg",p_ph_bkg) ;

  // Construct the joint model
  RooProdPdf model1("model1","model1",RooArgSet(hc_sig,hc_bkg),Conditional(model_tmp,w::x)) ;

  // ***** Case 2 - 'Beeston Barlow' light *****

  // Construct the background histogram shape, using the same parameters as the signal histogram 
  RooParamHistFunc p_ph_bkg2("p_ph_bkg","p_ph_bkg",*dh_bkg,p_ph_sig,1) ;  

  // Construct the sum of signal and background2 
  RooRealSumPdf model2_tmp("sp_ph","sp_ph",RooArgList(p_ph_sig,p_ph_bkg2),RooArgList(Asig,Abkg),kTRUE) ;

  // Construct the subsidiary poisson measurements constraining the sum of the histograms
  RooHistConstraint hc_sigbkg("hc_sigbkg","hc_sigbkg",RooArgSet(p_ph_sig,p_ph_bkg2)) ;

  // Construct the joint model
  RooProdPdf model2("model2","model2",hc_sigbkg,Conditional(model2_tmp,w::x)) ;



  model0.fitTo(*obsData) ;
  Double_t asig_val0 = Asig.getVal() ; Double_t asig_err0 = Asig.getError() ;
  model1.fitTo(*obsData) ;
  Double_t asig_val1 = Asig.getVal() ; Double_t asig_err1 = Asig.getError() ;
  model2.fitTo(*obsData) ;
  Double_t asig_val2 = Asig.getVal() ; Double_t asig_err2 = Asig.getError() ;
  
  cout << "Asig [normal ] = " << asig_val0 << " +/- " << asig_err0 << endl ;
  cout << "Asig [BB     ] = " << asig_val1 << " +/- " << asig_err1 << endl ;
  cout << "Asig [BBlight] = " << asig_val2 << " +/- " << asig_err2 << endl ;

}