//____________________________________
void DoHypothesisTest(RooWorkspace* wks){
// Use a RooStats ProfileLikleihoodCalculator to do the hypothesis test.
ModelConfig model;
model.SetWorkspace(*wks);
model.SetPdf("model");
//plc.SetData("data");
ProfileLikelihoodCalculator plc;
plc.SetData( *(wks->data("data") ));
// here we explicitly set the value of the parameters for the null.
// We want no signal contribution, eg. mu = 0
RooRealVar* mu = wks->var("mu");
// RooArgSet* nullParams = new RooArgSet("nullParams");
// nullParams->addClone(*mu);
RooArgSet poi(*mu);
RooArgSet * nullParams = (RooArgSet*) poi.snapshot();
nullParams->setRealValue("mu",0);
//plc.SetNullParameters(*nullParams);
plc.SetModel(model);
// NOTE: using snapshot will import nullparams
// in the WS and merge with existing "mu"
// model.SetSnapshot(*nullParams);
//use instead setNuisanceParameters
plc.SetNullParameters( *nullParams);
// We get a HypoTestResult out of the calculator, and we can query it.
HypoTestResult* htr = plc.GetHypoTest();
cout << "-------------------------------------------------" << endl;
cout << "The p-value for the null is " << htr->NullPValue() << endl;
cout << "Corresponding to a signifcance of " << htr->Significance() << endl;
cout << "-------------------------------------------------\n\n" << endl;
}
void exercise_3() {
//Open the rootfile and get the workspace from the exercise_0
TFile fIn("exercise_0.root");
fIn.cd();
RooWorkspace *w = (RooWorkspace*)fIn.Get("w");
//You can set constant parameters that are known
//If you leave them floating, the fit procedure will determine their uncertainty
w->var("mean")->setConstant(kFALSE); //don't fix the mean, it's what we want to know the interval for!
w->var("sigma")->setConstant(kTRUE);
w->var("tau")->setConstant(kTRUE);
w->var("Nsig")->setConstant(kTRUE);
w->var("Nbkg")->setConstant(kTRUE);
//Set the RooModelConfig and let it know what the content of the workspace is about
ModelConfig model;
model.SetWorkspace(*w);
model.SetPdf("PDFtot");
//Let the model know what is the parameter of interest
RooRealVar* mean = w->var("mean");
mean->setRange(120., 130.); //this is mostly for plotting reasons
RooArgSet poi(*mean);
// set confidence level
double confidenceLevel = 0.68;
//Build the profile likelihood calculator
ProfileLikelihoodCalculator plc;
plc.SetData(*(w->data("PDFtotData")));
plc.SetModel(model);
plc.SetParameters(poi);
plc.SetConfidenceLevel(confidenceLevel);
//Get the interval
LikelihoodInterval* plInt = plc.GetInterval();
//Now let's do the same for the Bayesian Calculator
//Now we also need to specify a prior in the ModelConfig
//To be quicker, we'll use the PDF factory facility of RooWorkspace
//NB!! For simplicity, we are using a flat prior, but this doesn't mean it's the best choice!
w->factory("Uniform::prior(mean)");
model.SetPriorPdf(*w->pdf("prior"));
//Construct the bayesian calculator
BayesianCalculator bc(*(w->data("PDFtotData")), model);
bc.SetConfidenceLevel(confidenceLevel);
bc.SetParameters(poi);
SimpleInterval* bcInt = bc.GetInterval();
// Let's make a plot
TCanvas dataCanvas("dataCanvas");
dataCanvas.Divide(2,1);
dataCanvas.cd(1);
LikelihoodIntervalPlot plotInt((LikelihoodInterval*)plInt);
plotInt.SetTitle("Profile Likelihood Ratio and Posterior for mH");
plotInt.SetMaximum(3.);
plotInt.Draw();
dataCanvas.cd(2);
RooPlot *bcPlot = bc.GetPosteriorPlot();
bcPlot->Draw();
dataCanvas.SaveAs("exercise_3.gif");
//Now print the interval for mH for the two methods
cout << "PLC interval is [" << plInt->LowerLimit(*mean) << ", " <<
plInt->UpperLimit(*mean) << "]" << endl;
cout << "Bayesian interval is [" << bcInt->LowerLimit() << ", " <<
bcInt->UpperLimit() << "]" << endl;
}