doc/v626/FitHistoInFile_8C.html

/// Based on FittingDemo.C by Rene Brun


#include "TH1.h"

#include "TMath.h"

#include "TF1.h"

#include "TLegend.h"

#include "TCanvas.h"

#include "TFile.h"

#include "TStyle.h"


// Function parameters are passed as an array to TF1. Here, we

// define the position of each parameter in this array.

// Note: N_PAR will give us the total number of parameters. Make

// sure it is always the last entry!

enum ParIndex_t {

   Bkg0=0, Bkg1=1, Bkg2,

   SigScale, SigSigma, SigMean,

   N_PAR};

// Use this map to (re-)name parameters for the plot

const std::map<ParIndex_t,std::string> parNames{

   {Bkg0, "Bkg0"}, {Bkg1, "Bkg1"}, {Bkg2, "Bkg2"},

   {SigScale, "Gauss scale"}, {SigSigma, "Gauss #sigma"}, {SigMean, "Gauss #mu"}

};


// Quadratic background function

Double_t background(Double_t *x, Double_t *par) {

   return par[Bkg0] + par[Bkg1]*x[0] + par[Bkg2]*x[0]*x[0];

}


// Gauss Peak function

Double_t signal(Double_t *x, Double_t *par) {

   return par[SigScale]*TMath::Gaus(x[0], par[SigMean], par[SigSigma], true);

}


// Sum of background and peak function. We pass x and the fit parameters

// down to the signal and background functions.

Double_t fitFunction(Double_t *x, Double_t *par) {

   return background(x, par) + signal(x, par);

}


// Fit "fitFunction" to the histogram, and draw results on the canvas `c1`.

void FitRoutine(TCanvas* c1, TH1* histo, float fitxmin, float fitxmax, TString filename){

   c1->cd();

   // create a TF1 with the range from 0 to 3 and N_PAR parameters (six by default)

   TF1 fitFcn("fitFcn",fitFunction,fitxmin,fitxmax,N_PAR);

   fitFcn.SetNpx(500);

   fitFcn.SetLineWidth(2);

   fitFcn.SetLineColor(kBlue);


   // Assign the names from the map "parNames". Optional, but makes a nicer plot.

   for (auto& idx_name : parNames) {

     fitFcn.SetParName(idx_name.first, idx_name.second.c_str());

   }


   // Fit. First set ok-ish starting values for the parameters

   fitFcn.SetParameters(30,0,0,50.,0.1,1.);

   histo->GetXaxis()->SetRange(2,40);

   histo->Fit("fitFcn","VR+","ep");


   // improve the picture:

   // Draw signal and background functions separately

   TF1 backFcn("backFcn",background,fitxmin,fitxmax,N_PAR);

   backFcn.SetLineColor(kRed);

   TF1 signalFcn("signalFcn",signal,fitxmin,fitxmax,N_PAR);

   signalFcn.SetLineColor(kBlue);

   signalFcn.SetNpx(500);


   // Retrieve fit parameters, and copy them to the signal and background functions

   Double_t par[N_PAR];

   fitFcn.GetParameters(par);


   backFcn.SetParameters(par);

   backFcn.DrawCopy("same");


   signalFcn.SetParameters(par);

   signalFcn.SetLineColor(kGreen);

   signalFcn.DrawCopy("same");


   const double binwidth = histo->GetXaxis()->GetBinWidth(1);

   const double integral = signalFcn.Integral(0.,3.);

   cout << "number of signal events = " << integral/binwidth << " " << binwidth<< endl;


   // draw the legend

   TLegend legend(0.15,0.7,0.28,0.85);

   legend.SetTextFont(72);

   legend.SetTextSize(0.03);

   legend.AddEntry(histo,"Data","lpe");

   legend.AddEntry(&backFcn,"Bgd","l");

   legend.AddEntry(&signalFcn,"Sig","l");

   legend.AddEntry(&fitFcn,"Sig+Bgd","l");

   legend.DrawClone();

   histo->Draw("esame");

   c1->SaveAs(filename);

}


// Create a file with example data

void CreateRootFile(){

   // The data in array form

   const int nBins = 60;

   Double_t data[nBins] = { 6, 1,10,12, 6,13,23,22,15,21,

                           23,26,36,25,27,35,40,44,66,81,

                           75,57,43,37,36,31,35,36,43,32,

                           40,37,38,33,36,44,42,37,32,32,

                           43,44,35,33,33,39,29,41,32,44,

                           26,39,29,35,32,21,21,15,25,15};


   TFile* f = new TFile("exampleRootFile.root","RECREATE");

   TH1D *histo = new TH1D("histo", "Gauss Peak on Quadratic Background;x;Events/0.05",60,0,3);

   for(int i=0; i < nBins;  i++) histo->SetBinContent(i+1,data[i]);

   f->Write();

   f->Close();

}


// Show how to fit a histogram that's in a file.

void FitHistoInFile() {

   gStyle->SetOptFit(1111);

   gStyle->SetOptStat(0);


   // fit range from fitxmin to fitxmax

   float fitxmin=0.2;

   float fitxmax=2.7;


   TCanvas *c1 = new TCanvas("c1","Fitting Demo of Histogram in File",10,10,700,500);

   CreateRootFile();

   TFile* f = new TFile("exampleRootFile.root");

   TH1D* histo= nullptr;

   f->GetObject("histo",histo);

   if (!histo){

      cout << "histo not found"<<endl;

      return;

   }

   histo->SetMarkerStyle(21);

   histo->SetMarkerSize(0.8);

   // now call the fit routine

   FitRoutine(c1,histo, fitxmin, fitxmax,"FitHistoInFile.pdf");

}

f
#define f(i)
Definition RSha256.hxx:104

Double_t
double Double_t
Definition RtypesCore.h:59

kRed
@ kRed
Definition Rtypes.h:66

kGreen
@ kGreen
Definition Rtypes.h:66

kBlue
@ kBlue
Definition Rtypes.h:66

TCanvas.h

TF1.h

TFile.h

TH1.h

TLegend.h

TMath.h

TStyle.h

gStyle
R__EXTERN TStyle * gStyle
Definition TStyle.h:413

TAttMarker::SetMarkerStyle
virtual void SetMarkerStyle(Style_t mstyle=1)
Set the marker style.
Definition TAttMarker.h:40

TAttMarker::SetMarkerSize
virtual void SetMarkerSize(Size_t msize=1)
Set the marker size.
Definition TAttMarker.h:41

TAxis::SetRange
virtual void SetRange(Int_t first=0, Int_t last=0)
Set the viewing range for the axis using bin numbers.
Definition TAxis.cxx:920

TAxis::GetBinWidth
virtual Double_t GetBinWidth(Int_t bin) const
Return bin width.
Definition TAxis.cxx:540

TCanvas
The Canvas class.
Definition TCanvas.h:23

TF1
1-Dim function class
Definition TF1.h:213

TFile
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition TFile.h:54

TH1D
1-D histogram with a double per channel (see TH1 documentation)}
Definition TH1.h:618

TH1
TH1 is the base class of all histogram classes in ROOT.
Definition TH1.h:58

TH1::GetXaxis
TAxis * GetXaxis()
Get the behaviour adopted by the object about the statoverflows. See EStatOverflows for more informat...
Definition TH1.h:320

TH1::Fit
virtual TFitResultPtr Fit(const char *formula, Option_t *option="", Option_t *goption="", Double_t xmin=0, Double_t xmax=0)
Fit histogram with function fname.
Definition TH1.cxx:3893

TH1::SetBinContent
virtual void SetBinContent(Int_t bin, Double_t content)
Set bin content see convention for numbering bins in TH1::GetBin In case the bin number is greater th...
Definition TH1.cxx:9052

TH1::Draw
virtual void Draw(Option_t *option="")
Draw this histogram with options.
Definition TH1.cxx:3074

TLegend
This class displays a legend box (TPaveText) containing several legend entries.
Definition TLegend.h:23

TString
Basic string class.
Definition TString.h:136

TStyle::SetOptStat
void SetOptStat(Int_t stat=1)
The type of information printed in the histogram statistics box can be selected via the parameter mod...
Definition TStyle.cxx:1589

TStyle::SetOptFit
void SetOptFit(Int_t fit=1)
The type of information about fit parameters printed in the histogram statistics box can be selected ...
Definition TStyle.cxx:1541

c1
return c1
Definition legend1.C:41

x
Double_t x[n]
Definition legend1.C:17

TMath::Gaus
Double_t Gaus(Double_t x, Double_t mean=0, Double_t sigma=1, Bool_t norm=kFALSE)
Calculate a gaussian function with mean and sigma.
Definition TMath.cxx:448