use noRounding for the Poisson of the sidebands since the noff value can be in...

use noRounding for the Poisson of the sidebands since the noff value can be in some cause non-integer (i.e. be interpreted as a Gamma constraint)


git-svn-id: http://root.cern.ch/svn/root/trunk@43932 27541ba8-7e3a-0410-8455-c3a389f83636

roofit/roostats/src/NumberCountingPdfFactory.cxx

@@ -133,8 +133,10 @@ void NumberCountingPdfFactory::AddModel(Double_t* sig,
 
       RooPoisson* sigRegion = 
          new RooPoisson(("sigRegion"+str.str()).c_str(),("sigRegion"+str.str()).c_str(), *x,*splusb);
+
+      //LM:  need to set noRounding since y can take non integer values
       RooPoisson* sideband = 
-         new RooPoisson(("sideband"+str.str()).c_str(),("sideband"+str.str()).c_str(), *y,*bTau);
+         new RooPoisson(("sideband"+str.str()).c_str(),("sideband"+str.str()).c_str(), *y,*bTau,true);
 
       likelihoodFactors.Add(sigRegion);
       likelihoodFactors.Add(sideband);
@@ -245,7 +247,11 @@ void NumberCountingPdfFactory::AddData(Double_t* mainMeas,
       std::stringstream str;
       str<<"_"<<i;
 
-      Double_t _tau = 1./back[i]/back_syst[i]/back_syst[i];
+      //Double_t _tau = 1./back[i]/back_syst[i]/back_syst[i];
+      // LM: compute tau correctly for the Gamma distribution : mode = tau*b  and variance is (tau*b+1)
+      Double_t err = back_syst[i]; 
+      Double_t _tau = (1.0 + sqrt(1 + 4 * err * err))/ (2. * err * err)/ back[i];
+
       RooRealVar*  tau = SafeObservableCreation(ws,  ("tau"+str.str()).c_str(), _tau );
 
       oocoutW(ws,ObjectHandling) << "NumberCountingPdfFactory: changed value of " << tau->GetName() << " to " << tau->getVal() <<