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Reference Guide
rf212_plottingInRanges_blinding.C
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1 /// \file
2 /// \ingroup tutorial_roofit
3 /// \notebook -js
4 ///
5 /// Plot a PDF in disjunct ranges, and get normalisation right.
6 ///
7 /// Usually, when comparing a fit to data, one should first plot the data, and then the PDF.
8 /// In this case, the PDF is automatically normalised to match the number of data events in the plot.
9 /// However, when plotting only a sub-range, when e.g. a signal region has to be blinded,
10 /// one has to exclude the blinded region from the computation of the normalisation.
11 ///
12 /// In this tutorial, we show how to explicitly choose the normalisation when plotting using `NormRange()`.
13 ///
14 /// Thanks to Marc Escalier for asking how to do this correctly.
15 ///
16 /// \macro_image
17 /// \macro_code
18 /// \macro_output
19 ///
20 /// \date 03/2020
21 /// \author Stephan Hageboeck
22 
23 #include <RooDataSet.h>
24 #include <RooExponential.h>
25 #include <RooPlot.h>
26 #include <RooRealVar.h>
27 #include <TCanvas.h>
28 
29 using namespace RooFit;
30 
31 void rf212_plottingInRanges_blinding()
32 {
33  // Make a fit model
34  RooRealVar x("x", "The observable", 1, 30);
35  RooRealVar tau("tau", "The exponent", -0.1337, -10., -0.1);
36  RooExponential exp("exp", "A falling exponential function", x, tau);
37 
38  // Define the sidebands (e.g. background regions)
39  x.setRange("full", 1, 30);
40  x.setRange("left", 1, 10);
41  x.setRange("right", 20, 30);
42 
43  // Generate toy data, and cut out the blinded region.
44  RooDataSet* data = exp.generate(x, 1000);
45  auto blindedData = data->reduce(CutRange("left,right"));
46 
47  // Kick tau a bit, and run an unbinned fit where the blinded data are missing.
48  // ----------------------------------------------------------------------------------------------------------
49  tau.setVal(-2.);
50  exp.fitTo(*blindedData);
51 
52 
53  // Here we will plot the results
54  TCanvas *canvas=new TCanvas("canvas","canvas",800,600);
55  canvas->Divide(2,1);
56 
57 
58  // Wrong:
59  // Plotting each slice on its own normalises the PDF over its plotting range. For the full curve, that means
60  // that the blinded region where data is missing is included in the normalisation calculation. The PDF therefore
61  // comes out too low, and doesn't match up with the slices in the side bands, which are normalised to "their" data.
62  // ----------------------------------------------------------------------------------------------------------
63 
64  std::cout << "Now plotting with unique normalisation for each slice." << std::endl;
65  canvas->cd(1);
66  RooPlot* plotFrame = x.frame(RooFit::Title("Wrong: Each slice normalised over its plotting range"));
67 
68  // Plot only the blinded data, and then plot the PDF over the full range as well as both sidebands
69  blindedData->plotOn(plotFrame);
70  exp.plotOn(plotFrame, LineColor(kRed), Range("full"));
71  exp.plotOn(plotFrame, LineColor(kBlue), Range("left"));
72  exp.plotOn(plotFrame, LineColor(kGreen), Range("right"));
73 
74  plotFrame->Draw();
75 
76  // Right:
77  // Make the same plot, but normalise each piece with respect to the regions "left" AND "right". This requires setting
78  // a "NormRange", which tells RooFit over which range the PDF has to be integrated to normalise.
79  // This is means that the normalisation of the blue and green curves is slightly different from the left plot,
80  // because they get a common scale factor.
81  // ----------------------------------------------------------------------------------------------------------
82 
83  std::cout << "\n\nNow plotting with correct norm ranges:" << std::endl;
84  canvas->cd(2);
85  RooPlot* plotFrameWithNormRange = x.frame(RooFit::Title("Right: All slices have common normalisation"));
86 
87  // Plot only the blinded data, and then plot the PDF over the full range as well as both sidebands
88  blindedData->plotOn(plotFrameWithNormRange);
89  exp.plotOn(plotFrameWithNormRange, LineColor(kBlue), Range("left"), RooFit::NormRange("left,right"));
90  exp.plotOn(plotFrameWithNormRange, LineColor(kGreen), Range("right"), RooFit::NormRange("left,right"));
91  exp.plotOn(plotFrameWithNormRange, LineColor(kRed), Range("full"), RooFit::NormRange("left,right"), LineStyle(10));
92 
93  plotFrameWithNormRange->Draw();
94 
95  canvas->Draw();
96 
97 }
RooPlot::Draw
virtual void Draw(Option_t *options=0)
Draw this plot and all of the elements it contains.
Definition: RooPlot.cxx:691
kGreen
@ kGreen
Definition: Rtypes.h:66
exp
double exp(double)
x
Double_t x[n]
Definition: legend1.C:17
TPad::Divide
virtual void Divide(Int_t nx=1, Int_t ny=1, Float_t xmargin=0.01, Float_t ymargin=0.01, Int_t color=0)
Automatic pad generation by division.
Definition: TPad.cxx:1166
TCanvas.h
RooDataSet.h
RooFit::CutRange
RooCmdArg CutRange(const char *rangeName)
Definition: RooGlobalFunc.cxx:88
TCanvas::Draw
virtual void Draw(Option_t *option="")
Draw a canvas.
Definition: TCanvas.cxx:841
RooFit
Definition: RooCFunction1Binding.h:29
TCanvas::cd
TVirtualPad * cd(Int_t subpadnumber=0)
Set current canvas & pad.
Definition: TCanvas.cxx:704
RooPlot.h
RooPlot
Definition: RooPlot.h:44
RooRealVar.h
kRed
@ kRed
Definition: Rtypes.h:66
RooExponential.h
RooFit::LineColor
RooCmdArg LineColor(Color_t color)
Definition: RooGlobalFunc.cxx:56
TCanvas
Definition: TCanvas.h:23
RooAbsData::reduce
RooAbsData * reduce(const RooCmdArg &arg1, const RooCmdArg &arg2=RooCmdArg(), const RooCmdArg &arg3=RooCmdArg(), const RooCmdArg &arg4=RooCmdArg(), const RooCmdArg &arg5=RooCmdArg(), const RooCmdArg &arg6=RooCmdArg(), const RooCmdArg &arg7=RooCmdArg(), const RooCmdArg &arg8=RooCmdArg())
Create a reduced copy of this dataset.
Definition: RooAbsData.cxx:382
RooFit::NormRange
RooCmdArg NormRange(const char *rangeNameList)
Definition: RooGlobalFunc.cxx:54
RooFit::Range
RooCmdArg Range(const char *rangeName, Bool_t adjustNorm=kTRUE)
Definition: RooGlobalFunc.cxx:52
kBlue
@ kBlue
Definition: Rtypes.h:66
RooDataSet
Definition: RooDataSet.h:33
RooFit::LineStyle
RooCmdArg LineStyle(Style_t style)
Definition: RooGlobalFunc.cxx:57
RooRealVar
Definition: RooRealVar.h:35
RooExponential
Definition: RooExponential.h:25
RooFit::Title
RooCmdArg Title(const char *name)
Definition: RooGlobalFunc.cxx:173