// make and test  Poisson model

using namespace RooFit; 
using namespace RooStats;

void makeCountingModel(int nobs = 40, double b = 20, double berr = 3) { 

   TString fname = TString::Format("countingmodel_n%d_b%d.root",nobs,int(b));
   TFile f(fname,"RECREATE");

   RooWorkspace* w = new RooWorkspace("w",true);
   w->factory("sum:nexp(s[1.,0,100],b[0,100])");
   w->factory("Poisson:pdf(nobs[0,100],nexp)");
   w->factory("Gaussian:constraint(b,b_glob[10],sigmab[1])");
   w->factory("PROD:model(pdf,constraint)");

   // set input variables
   w->var("b_glob")->setVal(b);
   w->var("sigmab")->setVal(berr);
   w->var("nobs")->setVal(nobs);
   // make data set
   RooDataSet data("data","", *(w->var("nobs")) );
   data.add(*(w->var("nobs")) );
   w->import(data);


   ModelConfig * mc = new ModelConfig("ModelConfig",w);
   mc->SetPdf(*w->pdf("model"));
   mc->SetParametersOfInterest(*w->var("s"));
   mc->SetObservables(*w->var("nobs"));
   mc->SetSnapshot(*w->var("s"));
   mc->SetNuisanceParameters( *w->var("b"));
   mc->SetGlobalObservables( *w->var("b_glob"));

   w->import(*mc);

   w->Write();

   cout << "model written to file " << endl;
   f.Close();

}