CMS.RooFit in FWLite

Complete: 3

  • How to load libRooFit.so and libRooFitCore.so from FWLite:

  • How to fill a RooDataSet from PAT objects: once we are up and running in FWLite and can access CMS.RooFit, we can use CMS.RooFit to actually do something. There are several ways of doing that:
    • Iterate over PAT files, make histograms (like in StarterKit), and then create RooDataHist objects from TH1F's and fit and plot them in CMS.RooFit
    • Alternatively, we could iterate over the PAT collections in FWLite, and make a RooDataSet (which is like an ntuple), which we can then manipulate further in CMS.RooFit (e.g. in an unbinned likelihood fit)

Using FWLite and RooFit for a toy analysis

This is brief macro demonstrating what you have to do to run RooFit in FWLite. To run the macro, you need have the StarterKit Skim file in your path. You can use other data, but you may need to modify parts of the code appropriately (specifically the file and the getByLabel lines)

#include "DataFormats/FWLite/interface/Handle.h"

#if !defined(__CINT__) && !defined(__MAKECINT__)
#include "DataFormats/PatCandidates/interface/Muon.h"
#include "DataFormats/PatCandidates/interface/Tau.h"
#endif

#include <iostream>
#include <TFile.h>
#include <TH1D.h>
#include "BigHeader.h"
//We declare using for the specific things that we need to use to prevent polluting the namespace
using std::cout;
using std::vector;
using pat::Muon;
using pat::Tau;
using fwlite::Handle;
using fwlite::Event;
using namespace CMS.RooFit;

void print_plot(RooDataSet *dataSet, RooRealVar *printVar, const char* outname)
{
  RooPlot *genericFrame = printVar->frame();
  dataSet->plotOn(genericFrame);
  TCanvas genericCanvas;
  genericFrame->Draw();
  genericCanvas.SaveAs(outname);
}

void RooFWLite()
{
  //FWLite Stuff (open a file and get events from it)
  TFile  *file = new TFile("/uscms_data/d1/dbjergaa/part1_PatAnalyzerKitSkim.root");
  Event ev(file);
  //CMS.RooFit Stuff (variables, dataset, argument set)
  RooRealVar muPt("muPt", "Muon Transverse momentum", 0, 100, "GeV/c");
  RooRealVar muEta("muEta","Muon Eta",-3.1415,3.1415,"Rad");
  RooRealVar tauPt("tauPt","Tau Transverse momentum",0,100,"GeV/c");
  RooRealVar tauEta("tauEta","Tau Eta",-3.1415,3.1415,"Rad");

  RooArgSet varSet( muPt, muEta, tauPt, tauEta);
  RooDataSet toyDataSet("toyDataSet", "Taus and Muons", varSet);

  //Event Loop
  for( ev.toBegin(); !ev.atEnd(); ++ev) 
    {
      Handle<vector<Muon> > h_mu;
      Handle<vector<Tau> > h_tau;
      h_mu.getByLabel(ev,"selectedLayer1Muons");
      h_tau.getByLabel(ev,"selectedLayer1Taus");
      //loop over each muon and get required numbers
      for ( unsigned int i = 0; i < h_mu.ptr()->size();  ++i ) 
   {
     vector<Muon> const & muons = *h_mu;
     muPt.setVal(muons[i].pt());
     muEta.setVal(muons[i].eta());
          //update dataset with the latest data
     toyDataSet.add(varSet);
   }
      //loop over taus and get information
      for (unsigned int i = 0; i < h_tau.ptr()->size(); ++i)
   {
     vector<Tau> const & taus = *h_tau;
     tauPt.setVal(taus[i].pt());
     tauEta.setVal(taus[i].eta());
     toyDataSet.add(varSet);
   }
    }

  //
  // INSERT FIT CODE HERE
  //

  //Save plots of the data (and eventually fitting)
  print_plot(&toyDataSet,&muPt,"muPtResults.eps");
  print_plot(&toyDataSet,&muEta,"muEtaResults.eps");
  print_plot(&toyDataSet,&tauPt,"tauPtResults.eps");
  print_plot(&toyDataSet,&tauEta,"tauEtaResults.eps");

}
This will print 4 plots using the print_plot function which create plots to use in a talk etc. The quality of these plots are not that great by default, but it wouldn't be hard to implement a custom style to produce more attractive plots. To run this macro do:
$ root -l -b
root[] .L RooFWLite.C++
(compile output)
root[]  RooFWLite();

-- DavidBjergaard - 06 Jan 2009

-- PetarMaksimovic - 06 Jan 2009

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Topic revision: r1 - 2009-05-14 - LucaLista
 
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