ROOT   Reference Guide
rf109_chi2residpull.C File Reference

## Detailed Description

Basic functionality: Calculating chi^2 from histograms and curves in RooPlots, making histogram of residual and pull distributions

chi^2 = 2.63198
#include "RooRealVar.h"
#include "RooDataSet.h"
#include "RooGaussian.h"
#include "RooConstVar.h"
#include "TCanvas.h"
#include "TAxis.h"
#include "RooPlot.h"
#include "RooHist.h"
using namespace RooFit;
{
// 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.setVal(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()
cout << "chi^2 = " << frame1->chiSquare() << endl;
// 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"));
// Create a new frame to draw the pull distribution and add the distribution to the frame
RooPlot *frame3 = x.frame(Title("Pull Distribution"));
TCanvas *c = new TCanvas("rf109_chi2residpull", "rf109_chi2residpull", 900, 300);
c->Divide(3);
c->cd(1);
frame1->GetYaxis()->SetTitleOffset(1.6);
frame1->Draw();
c->cd(2);
frame2->GetYaxis()->SetTitleOffset(1.6);
frame2->Draw();
c->cd(3);
frame3->GetYaxis()->SetTitleOffset(1.6);
frame3->Draw();
}
#define c(i)
Definition: RSha256.hxx:101
Option_t Option_t TPoint TPoint const char GetTextMagnitude GetFillStyle GetLineColor GetLineWidth GetMarkerStyle GetTextAlign GetTextColor GetTextSize void data
RooDataSet is a container class to hold unbinned data.
Definition: RooDataSet.h:55
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:29
A RooPlot is a plot frame and a container for graphics objects within that frame.
Definition: RooPlot.h:43
void Draw(Option_t *options=0) override
Draw this plot and all of the elements it contains.
Definition: RooPlot.cxx:679
double chiSquare(int nFitParam=0) const
Shortcut for RooPlot::chiSquare(const char* pdfname, const char* histname, int nFitParam=nullptr)
Definition: RooPlot.h:177
TAxis * GetYaxis() const
Definition: RooPlot.cxx:1270
RooHist * residHist(const char *histname=nullptr, const char *pdfname=nullptr, bool normalize=false, bool useAverage=true) const
Return a RooHist (derives from TGraphAsymErrors) containing the residuals of a histogram.
Definition: RooPlot.cxx:1143
RooHist * pullHist(const char *histname=nullptr, const char *pdfname=nullptr, bool useAverage=true) const
Uses residHist() and sets normalize=true.
Definition: RooPlot.h:182
void addPlotable(RooPlotable *plotable, Option_t *drawOptions="", bool invisible=false, bool refreshNorm=false)
Add the specified plotable object to our plot.
Definition: RooPlot.cxx:558
RooRealVar represents a variable that can be changed from the outside.
Definition: RooRealVar.h:40
virtual void SetTitleOffset(Float_t offset=1)
Set distance between the axis and the axis title.
Definition: TAttAxis.cxx:301
The Canvas class.
Definition: TCanvas.h:23
RooConstVar & RooConst(double 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...
Definition: Common.h:18
static constexpr double gauss
const char * Title
Definition: TXMLSetup.cxx:68
Date
July 2008

Definition in file rf109_chi2residpull.C.