rf109_chi2residpull.cxx

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//////////////////////////////////////////////////////////////////////////
//
// 'BASIC FUNCTIONALITY' RooFit tutorial macro #109
// 
// Calculating chi^2 from histograms and curves in RooPlots, 
// making histogram of residual and pull distributions
//
//
//
// 07/2008 - Wouter Verkerke 
// 
/////////////////////////////////////////////////////////////////////////

#ifndef __CINT__
#include "RooGlobalFunc.h"
#endif
#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "TCanvas.h"
#include "RooPlot.h"
#include "RooHist.h"
using namespace RooFit ;

class TestBasic109 : public RooFitTestUnit
{
public: 
  TestBasic109(TFile* refFile, Bool_t writeRef, Int_t verbose) : RooFitTestUnit("Calculation of chi^2 and residuals in plots",refFile,writeRef,verbose) {} ;
  Bool_t testCode() {
    
    // S e t u p   m o d e l 
    // ---------------------
    
    // Create observables
    RooRealVar x("x","x",-10,10) ;
    
    // Create Gaussian
    RooRealVar sigma("sigma","sigma",3,0.1,10) ;
    RooRealVar mean("mean","mean",0,-10,10) ;
    RooGaussian gauss("gauss","gauss",x,RooConst(0),sigma) ;
    
    // Generate a sample of 1000 events with sigma=3
    RooDataSet* data = gauss.generate(x,10000) ;
    
    // Change sigma to 3.15
    sigma=3.15 ;
    
    
    // P l o t   d a t a   a n d   s l i g h t l y   d i s t o r t e d   m o d e l
    // ---------------------------------------------------------------------------
    
    // Overlay projection of gauss with sigma=3.15 on data with sigma=3.0
    RooPlot* frame1 = x.frame(Title("Data with distorted Gaussian pdf"),Bins(40)) ;
    data->plotOn(frame1,DataError(RooAbsData::SumW2)) ;
    gauss.plotOn(frame1) ;
    
    
    // C a l c u l a t e   c h i ^ 2 
    // ------------------------------
    
    // Show the chi^2 of the curve w.r.t. the histogram
    // If multiple curves or datasets live in the frame you can specify
    // the name of the relevant curve and/or dataset in chiSquare()
    regValue(frame1->chiSquare(),"rf109_chi2") ;
    
    
    // S h o w   r e s i d u a l   a n d   p u l l   d i s t s
    // -------------------------------------------------------
    
    // Construct a histogram with the residuals of the data w.r.t. the curve
    RooHist* hresid = frame1->residHist() ;
    
    // Construct a histogram with the pulls of the data w.r.t the curve
    RooHist* hpull = frame1->pullHist() ;
    
    // Create a new frame to draw the residual distribution and add the distribution to the frame
    RooPlot* frame2 = x.frame(Title("Residual Distribution")) ;
    frame2->addPlotable(hresid,"P") ;
    
    // Create a new frame to draw the pull distribution and add the distribution to the frame
    RooPlot* frame3 = x.frame(Title("Pull Distribution")) ;
    frame3->addPlotable(hpull,"P") ;
    
    regPlot(frame1,"rf109_plot1") ;
    regPlot(frame2,"rf109_plot2") ;
    regPlot(frame3,"rf109_plot3") ;

    delete data ;
    //delete hresid ;
    //delete hpull ;
    
    return kTRUE ;    
  }
} ;