 ROOT   Reference Guide rf212_plottingInRanges_blinding.C
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1 /// \file
2 /// \ingroup tutorial_roofit
3 /// \notebook -js
4 /// Plot a PDF in disjunct ranges, and get normalisation right.
5 ///
6 /// Usually, when comparing a fit to data, one should first plot the data, and then the PDF.
7 /// In this case, the PDF is automatically normalised to match the number of data events in the plot.
8 /// However, when plotting only a sub-range, when e.g. a signal region has to be blinded,
9 /// one has to exclude the blinded region from the computation of the normalisation.
10 ///
11 /// In this tutorial, we show how to explicitly choose the normalisation when plotting using NormRange().
12 ///
13 /// Thanks to Marc Escalier for asking how to do this correctly.
14 ///
15 /// \macro_image
16 /// \macro_code
17 /// \macro_output
18 ///
19 /// \date March 2020
20 /// \author Stephan Hageboeck
21
22 #include <RooDataSet.h>
23 #include <RooExponential.h>
24 #include <RooPlot.h>
25 #include <RooRealVar.h>
26 #include <TCanvas.h>
27
28 using namespace RooFit;
29
30 void rf212_plottingInRanges_blinding()
31 {
32  // Make a fit model
33  RooRealVar x("x", "The observable", 1, 30);
34  RooRealVar tau("tau", "The exponent", -0.1337, -10., -0.1);
35  RooExponential exp("exp", "A falling exponential function", x, tau);
36
37  // Define the sidebands (e.g. background regions)
38  x.setRange("full", 1, 30);
39  x.setRange("left", 1, 10);
40  x.setRange("right", 20, 30);
41
42  // Generate toy data, and cut out the blinded region.
43  RooDataSet* data = exp.generate(x, 1000);
44  auto blindedData = data->reduce(CutRange("left,right"));
45
46  // Kick tau a bit, and run an unbinned fit where the blinded data are missing.
47  // ----------------------------------------------------------------------------------------------------------
48  tau.setVal(-2.);
49  exp.fitTo(*blindedData);
50
51
52  // Here we will plot the results
53  TCanvas *canvas=new TCanvas("canvas","canvas",800,600);
54  canvas->Divide(2,1);
55
56
57  // Wrong:
58  // Plotting each slice on its own normalises the PDF over its plotting range. For the full curve, that means
59  // that the blinded region where data is missing is included in the normalisation calculation. The PDF therefore
60  // comes out too low, and doesn't match up with the slices in the side bands, which are normalised to "their" data.
61  // ----------------------------------------------------------------------------------------------------------
62
63  std::cout << "Now plotting with unique normalisation for each slice." << std::endl;
64  canvas->cd(1);
65  RooPlot* plotFrame = x.frame(RooFit::Title("Wrong: Each slice normalised over its plotting range"));
66
67  // Plot only the blinded data, and then plot the PDF over the full range as well as both sidebands
68  blindedData->plotOn(plotFrame);
69  exp.plotOn(plotFrame, LineColor(kRed), Range("full"));
70  exp.plotOn(plotFrame, LineColor(kBlue), Range("left"));
71  exp.plotOn(plotFrame, LineColor(kGreen), Range("right"));
72
73  plotFrame->Draw();
74
75  // Right:
76  // Make the same plot, but normalise each piece with respect to the regions "left" AND "right". This requires setting
77  // a "NormRange", which tells RooFit over which range the PDF has to be integrated to normalise.
78  // This is means that the normalisation of the blue and green curves is slightly different from the left plot,
79  // because they get a common scale factor.
80  // ----------------------------------------------------------------------------------------------------------
81
82  std::cout << "\n\nNow plotting with correct norm ranges:" << std::endl;
83  canvas->cd(2);
84  RooPlot* plotFrameWithNormRange = x.frame(RooFit::Title("Right: All slices have common normalisation"));
85
86  // Plot only the blinded data, and then plot the PDF over the full range as well as both sidebands
87  blindedData->plotOn(plotFrameWithNormRange);
88  exp.plotOn(plotFrameWithNormRange, LineColor(kBlue), Range("left"), RooFit::NormRange("left,right"));
89  exp.plotOn(plotFrameWithNormRange, LineColor(kGreen), Range("right"), RooFit::NormRange("left,right"));
90  exp.plotOn(plotFrameWithNormRange, LineColor(kRed), Range("full"), RooFit::NormRange("left,right"), LineStyle(10));
91
92  plotFrameWithNormRange->Draw();
93
94  canvas->Draw();
95
96 }
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
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)
TCanvas.h
RooDataSet.h
RooFit::CutRange
RooCmdArg CutRange(const char *rangeName)
Definition: RooGlobalFunc.cxx:89
TCanvas::Draw
virtual void Draw(Option_t *option="")
Draw a canvas.
Definition: TCanvas.cxx:845
RooFit
The namespace RooFit contains mostly switches that change the behaviour of functions of PDFs (or othe...
Definition: RooCFunction1Binding.h:29
TCanvas::cd
Definition: TCanvas.cxx:708
RooPlot.h
RooPlot
A RooPlot is a plot frame and a container for graphics objects within that frame.
Definition: RooPlot.h:44
RooRealVar.h
kRed
@ kRed
Definition: Rtypes.h:66
RooExponential.h
RooFit::LineColor
RooCmdArg LineColor(Color_t color)
Definition: RooGlobalFunc.cxx:57
TCanvas
The Canvas class.
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:55
RooFit::Range
RooCmdArg Range(const char *rangeName, Bool_t adjustNorm=kTRUE)
Definition: RooGlobalFunc.cxx:53
kBlue
@ kBlue
Definition: Rtypes.h:66
RooDataSet
RooDataSet is a container class to hold unbinned data.
Definition: RooDataSet.h:33
RooFit::LineStyle
RooCmdArg LineStyle(Style_t style)
Definition: RooGlobalFunc.cxx:58
RooRealVar
RooRealVar represents a variable that can be changed from the outside.
Definition: RooRealVar.h:37
RooExponential
Exponential PDF.
Definition: RooExponential.h:25
RooFit::Title
RooCmdArg Title(const char *name)
Definition: RooGlobalFunc.cxx:176