StandardTestStatDistributionDemo.C

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/// \file
/// \ingroup tutorial_roostats
/// \notebook
/// StandardTestStatDistributionDemo.C
///
/// This simple script plots the sampling distribution of the profile likelihood
/// ratio test statistic based on the input Model File.  To do this one needs to
/// specify the value of the parameter of interest that will be used for evaluating
/// the test statistic and the value of the parameters used for generating the toy data.
/// In this case, it uses the upper-limit estimated from the ProfileLikleihoodCalculator,
/// which assumes the asymptotic chi-square distribution for -2 log profile likelihood ratio.
/// Thus, the script is handy for checking to see if the asymptotic approximations are valid.
/// To aid, that comparison, the script overlays a chi-square distribution as well.
/// The most common parameter of interest is a parameter proportional to the signal rate,
/// and often that has a lower-limit of 0, which breaks the standard chi-square distribution.
/// Thus the script allows the parameter to be negative so that the overlay chi-square is
/// the correct asymptotic distribution.
///
/// \macro_image
/// \macro_output
/// \macro_code
///
/// \author Kyle Cranmer
 
#include "TFile.h"
#include "TROOT.h"
#include "TH1F.h"
#include "TCanvas.h"
#include "TSystem.h"
#include "TF1.h"
#include "TSystem.h"
 
#include "RooWorkspace.h"
#include "RooAbsData.h"
 
#include "RooStats/ModelConfig.h"
#include "RooStats/FeldmanCousins.h"
#include "RooStats/ToyMCSampler.h"
#include "RooStats/PointSetInterval.h"
#include "RooStats/ConfidenceBelt.h"
 
#include "RooStats/ProfileLikelihoodCalculator.h"
#include "RooStats/LikelihoodInterval.h"
#include "RooStats/ProfileLikelihoodTestStat.h"
#include "RooStats/SamplingDistribution.h"
#include "RooStats/SamplingDistPlot.h"
 
using namespace RooFit;
using namespace RooStats;
 
// -------------------------------------------------------
// The actual macro
 
void StandardTestStatDistributionDemo(const char *infile = "", const char *workspaceName = "combined",
                                      const char *modelConfigName = "ModelConfig", const char *dataName = "obsData")
{
 
   // the number of toy MC used to generate the distribution
   int nToyMC = 1000;
   // The parameter below is needed for asymptotic distribution to be chi-square,
   // but set to false if your model is not numerically stable if mu<0
   bool allowNegativeMu = true;
 
   // -------------------------------------------------------
   // First part is just to access a user-defined file
   // or create the standard example file if it doesn't exist
   const char *filename = "";
   if (!strcmp(infile, "")) {
      filename = "results/example_combined_GaussExample_model.root";
      bool fileExist = !gSystem->AccessPathName(filename); // note opposite return code
      // if file does not exists generate with histfactory
      if (!fileExist) {
         // Normally this would be run on the command line
         cout << "will run standard hist2workspace example" << endl;
         gROOT->ProcessLine(".! prepareHistFactory .");
         gROOT->ProcessLine(".! hist2workspace config/example.xml");
         cout << "\n\n---------------------" << endl;
         cout << "Done creating example input" << endl;
         cout << "---------------------\n\n" << endl;
      }
 
   } else
      filename = infile;
 
   // Try to open the file
   TFile *file = TFile::Open(filename);
 
   // if input file was specified but not found, quit
   if (!file) {
      cout << "StandardRooStatsDemoMacro: Input file " << filename << " is not found" << endl;
      return;
   }
 
   // -------------------------------------------------------
   // Now get the data and workspace
 
   // get the workspace out of the file
   RooWorkspace *w = (RooWorkspace *)file->Get(workspaceName);
   if (!w) {
      cout << "workspace not found" << endl;
      return;
   }
 
   // get the modelConfig out of the file
   ModelConfig *mc = (ModelConfig *)w->obj(modelConfigName);
 
   // get the modelConfig out of the file
   RooAbsData *data = w->data(dataName);
 
   // make sure ingredients are found
   if (!data || !mc) {
      w->Print();
      cout << "data or ModelConfig was not found" << endl;
      return;
   }
 
   mc->Print();
   // -------------------------------------------------------
   // Now find the upper limit based on the asymptotic results
   RooRealVar *firstPOI = (RooRealVar *)mc->GetParametersOfInterest()->first();
   ProfileLikelihoodCalculator plc(*data, *mc);
   LikelihoodInterval *interval = plc.GetInterval();
   double plcUpperLimit = interval->UpperLimit(*firstPOI);
   delete interval;
   cout << "\n\n--------------------------------------" << endl;
   cout << "Will generate sampling distribution at " << firstPOI->GetName() << " = " << plcUpperLimit << endl;
   int nPOI = mc->GetParametersOfInterest()->getSize();
   if (nPOI > 1) {
      cout << "not sure what to do with other parameters of interest, but here are their values" << endl;
      mc->GetParametersOfInterest()->Print("v");
   }
 
   // -------------------------------------------------------
   // create the test stat sampler
   ProfileLikelihoodTestStat ts(*mc->GetPdf());
 
   // to avoid effects from boundary and simplify asymptotic comparison, set min=-max
   if (allowNegativeMu)
      firstPOI->setMin(-1 * firstPOI->getMax());
 
   // temporary RooArgSet
   RooArgSet poi;
   poi.add(*mc->GetParametersOfInterest());
 
   // create and configure the ToyMCSampler
   ToyMCSampler sampler(ts, nToyMC);
   sampler.SetPdf(*mc->GetPdf());
   sampler.SetObservables(*mc->GetObservables());
   sampler.SetGlobalObservables(*mc->GetGlobalObservables());
   if (!mc->GetPdf()->canBeExtended() && (data->numEntries() == 1)) {
      cout << "tell it to use 1 event" << endl;
      sampler.SetNEventsPerToy(1);
   }
   firstPOI->setVal(plcUpperLimit);                                  // set POI value for generation
   sampler.SetParametersForTestStat(*mc->GetParametersOfInterest()); // set POI value for evaluation
 
   firstPOI->setVal(plcUpperLimit);
   RooArgSet allParameters;
   allParameters.add(*mc->GetParametersOfInterest());
   allParameters.add(*mc->GetNuisanceParameters());
   allParameters.Print("v");
 
   SamplingDistribution *sampDist = sampler.GetSamplingDistribution(allParameters);
   SamplingDistPlot plot;
   plot.AddSamplingDistribution(sampDist);
   plot.GetTH1F(sampDist)->GetYaxis()->SetTitle(
      Form("f(-log #lambda(#mu=%.2f) | #mu=%.2f)", plcUpperLimit, plcUpperLimit));
   plot.SetAxisTitle(Form("-log #lambda(#mu=%.2f)", plcUpperLimit));
 
   TCanvas *c1 = new TCanvas("c1");
   c1->SetLogy();
   plot.Draw();
   double min = plot.GetTH1F(sampDist)->GetXaxis()->GetXmin();
   double max = plot.GetTH1F(sampDist)->GetXaxis()->GetXmax();
 
   TF1 *f = new TF1("f", Form("2*ROOT::Math::chisquared_pdf(2*x,%d,0)", nPOI), min, max);
   f->Draw("same");
   c1->SaveAs("standard_test_stat_distribution.pdf");
}