using namespace RooFit;
using namespace RooStats;

void CountingModel(  int nobs = 0.177408,           // number of observed events
                     double b = 34830.16,           // number of background events
                     double sigmab = 44.57 )   // relative uncertainty in b//44.57
{
   RooWorkspace w("w");
   w.factory("sum:nexp(s[10,0,135],b[10,0,34900])");
   w.factory("Poisson:pdf(nobs[0,70],nexp)");
   w.factory("Gaussian:constraint(b0[0,45],b,sigmab[1])");
   w.factory("PROD:model(pdf,constraint)");

   w.var("b0")->setVal(b);
   w.var("b0")->setConstant(true); // needed for being treated as global observables
   w.var("sigmab")->setVal(sigmab*b);  

   ModelConfig mc("ModelConfig",&w);
   mc.SetPdf(*w.pdf("model"));
   mc.SetParametersOfInterest(*w.var("s"));
   mc.SetObservables(*w.var("nobs"));
   mc.SetNuisanceParameters(*w.var("b"));
   mc.SetSnapshot(*w.var("s"));
   mc.SetGlobalObservables(*w.var("b0"));
   mc.Print();

   w.import(mc);
   RooDataSet data("data","", *w.var("nobs"));

float data_var = nobs*23/37 ;// 23/37


   w.var("nobs")->setVal(data_var);

   data.add(*w.var("nobs") );

   w.import(data);
   w.Print();

   TString fileName = "CountingModel.root"; 
   w.writeToFile(fileName, true);

}