StandardBayesianNumericalDemo.C

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// Standard demo of the numerical Bayesian calculator

/*


Author: Kyle Cranmer
date: Dec. 2010

This is a standard demo that can be used with any ROOT file 
prepared in the standard way.  You specify:
 - name for input ROOT file
 - name of workspace inside ROOT file that holds model and data
 - name of ModelConfig that specifies details for calculator tools
 - name of dataset 

With default parameters the macro will attempt to run the 
standard hist2workspace example and read the ROOT file
that it produces.

The actual heart of the demo is only about 10 lines long.

The BayesianCalculator is based on Bayes's theorem
and performs the integration using ROOT's numeric integration utilities
*/

#include "TFile.h"
#include "TROOT.h"
#include "RooWorkspace.h"
#include "RooAbsData.h"
#include "RooRealVar.h"

#include "RooUniform.h"
#include "RooStats/ModelConfig.h"
#include "RooStats/BayesianCalculator.h"
#include "RooStats/SimpleInterval.h"
#include "RooPlot.h"

using namespace RooFit;
using namespace RooStats;

void StandardBayesianNumericalDemo(const char* infile = "",
                      const char* workspaceName = "proto",
                      const char* modelConfigName = "ModelConfig",
                      const char* dataName = "expData"){

  /////////////////////////////////////////////////////////////
  // First part is just to access a user-defined file 
  // or create the standard example file if it doesn't exist
  ////////////////////////////////////////////////////////////

  // note, use a different default file that BayesianCalculator can 
  // deal with.  The direct numeric integration is limited to a few dimensions
  const char* filename = "";
  if (!strcmp(infile,"")) 
    filename = "results/example_channel1_ConstExample_model.root";
  else
    filename = infile;
  // Check if example input file exists
  TFile *file = TFile::Open(filename);

  // if input file was specified byt not found, quit
  if(!file && strcmp(infile,"")){
    cout <<"file not found" << endl;
    return;
  } 

  // if default file not found, try to create it
  if(!file ){
    // 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;
  }

  // now try to access the file again
  file = TFile::Open(filename);
  if(!file){
    // if it is still not there, then we can't continue
    cout << "Not able to run hist2workspace to create example input" <<endl;
    return;
  }

  
  /////////////////////////////////////////////////////////////
  // Tutorial starts here
  ////////////////////////////////////////////////////////////

  // 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;
  }

  /////////////////////////////////////////////
  // create and use the BayesianCalculator
  // to find and plot the 95% credible interval
  // on the parameter of interest as specified
  // in the model config
  
  // before we do that, we must specify our prior
  // it belongs in the model config, but it may not have
  // been specified
  RooUniform prior("prior","",*mc->GetParametersOfInterest());
  w->import(prior);
  mc->SetPriorPdf(*w->pdf("prior"));

  
  BayesianCalculator bayesianCalc(*data,*mc);
  bayesianCalc.SetConfidenceLevel(0.95); // 95% interval

  // default is the shortest interval.  here use central
  bayesianCalc.SetLeftSideTailFraction(0.5); // for central interval

  SimpleInterval* interval = bayesianCalc.GetInterval();

  // make a plot (slightly inconsistent interface)
  // since plotting may take a long time (it requires evaluating 
  // the posterior in many points) this command will speed up 
  // by reducing the number of points to plot - do 40
  bayesianCalc.SetScanOfPosterior(40);
  RooPlot * plot = bayesianCalc.GetPosteriorPlot();
  plot->Draw();
  
  // print out the iterval on the first Parameter of Interest
  RooRealVar* firstPOI = (RooRealVar*) mc->GetParametersOfInterest()->first();
  cout << "\n95% interval on " <<firstPOI->GetName()<<" is : ["<<
    interval->LowerLimit() << ", "<<
    interval->UpperLimit() <<"] "<<endl;

}

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