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Reference Guide
rf109_chi2residpull.C
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1/// \file
2/// \ingroup tutorial_roofit
3/// \notebook -js
4/// Basic functionality: Calculating chi^2 from histograms and curves in RooPlots, making
5/// histogram of residual and pull distributions
6///
7/// \macro_image
8/// \macro_output
9/// \macro_code
10///
11/// \date July 2008
12/// \author Wouter Verkerke
13
14#include "RooRealVar.h"
15#include "RooDataSet.h"
16#include "RooGaussian.h"
17#include "RooConstVar.h"
18#include "TCanvas.h"
19#include "TAxis.h"
20#include "RooPlot.h"
21#include "RooHist.h"
22using namespace RooFit;
23
24void rf109_chi2residpull()
25{
26
27 // S e t u p m o d e l
28 // ---------------------
29
30 // Create observables
31 RooRealVar x("x", "x", -10, 10);
32
33 // Create Gaussian
34 RooRealVar sigma("sigma", "sigma", 3, 0.1, 10);
35 RooRealVar mean("mean", "mean", 0, -10, 10);
36 RooGaussian gauss("gauss", "gauss", x, RooConst(0), sigma);
37
38 // Generate a sample of 1000 events with sigma=3
39 RooDataSet *data = gauss.generate(x, 10000);
40
41 // Change sigma to 3.15
42 sigma = 3.15;
43
44 // 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
45 // ---------------------------------------------------------------------------
46
47 // Overlay projection of gauss with sigma=3.15 on data with sigma=3.0
48 RooPlot *frame1 = x.frame(Title("Data with distorted Gaussian pdf"), Bins(40));
49 data->plotOn(frame1, DataError(RooAbsData::SumW2));
50 gauss.plotOn(frame1);
51
52 // C a l c u l a t e c h i ^ 2
53 // ------------------------------
54
55 // Show the chi^2 of the curve w.r.t. the histogram
56 // If multiple curves or datasets live in the frame you can specify
57 // the name of the relevant curve and/or dataset in chiSquare()
58 cout << "chi^2 = " << frame1->chiSquare() << endl;
59
60 // S h o w r e s i d u a l a n d p u l l d i s t s
61 // -------------------------------------------------------
62
63 // Construct a histogram with the residuals of the data w.r.t. the curve
64 RooHist *hresid = frame1->residHist();
65
66 // Construct a histogram with the pulls of the data w.r.t the curve
67 RooHist *hpull = frame1->pullHist();
68
69 // Create a new frame to draw the residual distribution and add the distribution to the frame
70 RooPlot *frame2 = x.frame(Title("Residual Distribution"));
71 frame2->addPlotable(hresid, "P");
72
73 // Create a new frame to draw the pull distribution and add the distribution to the frame
74 RooPlot *frame3 = x.frame(Title("Pull Distribution"));
75 frame3->addPlotable(hpull, "P");
76
77 TCanvas *c = new TCanvas("rf109_chi2residpull", "rf109_chi2residpull", 900, 300);
78 c->Divide(3);
79 c->cd(1);
80 gPad->SetLeftMargin(0.15);
81 frame1->GetYaxis()->SetTitleOffset(1.6);
82 frame1->Draw();
83 c->cd(2);
84 gPad->SetLeftMargin(0.15);
85 frame2->GetYaxis()->SetTitleOffset(1.6);
86 frame2->Draw();
87 c->cd(3);
88 gPad->SetLeftMargin(0.15);
89 frame3->GetYaxis()->SetTitleOffset(1.6);
90 frame3->Draw();
91}
#define c(i)
Definition: RSha256.hxx:101
#define gPad
Definition: TVirtualPad.h:287
virtual RooPlot * plotOn(RooPlot *frame, const RooCmdArg &arg1=RooCmdArg::none(), const RooCmdArg &arg2=RooCmdArg::none(), const RooCmdArg &arg3=RooCmdArg::none(), const RooCmdArg &arg4=RooCmdArg::none(), const RooCmdArg &arg5=RooCmdArg::none(), const RooCmdArg &arg6=RooCmdArg::none(), const RooCmdArg &arg7=RooCmdArg::none(), const RooCmdArg &arg8=RooCmdArg::none()) const
Definition: RooAbsData.cxx:547
RooDataSet is a container class to hold unbinned data.
Definition: RooDataSet.h:33
Plain Gaussian p.d.f.
Definition: RooGaussian.h:24
A RooHist is a graphical representation of binned data based on the TGraphAsymmErrors class.
Definition: RooHist.h:27
A RooPlot is a plot frame and a container for graphics objects within that frame.
Definition: RooPlot.h:44
RooHist * residHist(const char *histname=0, const char *pdfname=0, bool normalize=false, bool useAverage=true) const
Return a RooHist (derives from TGraphAsymErrors) containing the residuals of histogram 'histname' wit...
Definition: RooPlot.cxx:1138
Double_t chiSquare(int nFitParam=0) const
Shortcut for RooPlot::chiSquare(const char* pdfname, const char* histname, int nFitParam=0)
Definition: RooPlot.h:176
TAxis * GetYaxis() const
Definition: RooPlot.cxx:1263
void addPlotable(RooPlotable *plotable, Option_t *drawOptions="", Bool_t invisible=kFALSE, Bool_t refreshNorm=kFALSE)
Add the specified plotable object to our plot.
Definition: RooPlot.cxx:570
virtual void Draw(Option_t *options=0)
Draw this plot and all of the elements it contains.
Definition: RooPlot.cxx:691
RooHist * pullHist(const char *histname=0, const char *pdfname=0, bool useAverage=true) const
Uses residHist() and sets normalize=true.
Definition: RooPlot.h:181
RooRealVar represents a variable that can be changed from the outside.
Definition: RooRealVar.h:39
virtual void SetTitleOffset(Float_t offset=1)
Set distance between the axis and the axis title.
Definition: TAttAxis.cxx:293
The Canvas class.
Definition: TCanvas.h:23
RooConstVar & RooConst(Double_t val)
RooCmdArg Bins(Int_t nbin)
RooCmdArg DataError(Int_t)
const Double_t sigma
Double_t x[n]
Definition: legend1.C:17
The namespace RooFit contains mostly switches that change the behaviour of functions of PDFs (or othe...
static constexpr double gauss
const char * Title
Definition: TXMLSetup.cxx:68