NormalizeHistogram.C

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/// \file
/// \ingroup tutorial_hist
/// \notebook -js
/// Normalizing a Histogram
///
/// Image produced by `.x NormalizeHistogram.C`
/// Two different methods of normalizing histograms
/// are shown, each with the original histogram.
/// next to the normalized one.
/// \macro_image
/// \macro_code
///
/// \author Advait Dhingra
 
#include "TH2F.h"
#include "TRandom.h"
#include "TCanvas.h"
 
void NormalizeHistogram()
{
 
   std::array<double, 6> binsx{0, 5, 10, 20, 50, 100};
   TH1F *orig = new TH1F("orig", "Original histogram before normalization", binsx.size() - 1, &binsx[0]);
 
   gStyle->SetTitleFontSize(0.06);
 
   TRandom2 rand;
 
   // Filling histogram with random entries
   for (int i = 0; i < 100'000; ++i) {
      double r = rand.Rndm() * 100;
      orig->Fill(r);
   }
 
   TH1F *norm = (TH1F *)orig->Clone("norm");
   norm->SetTitle("Normalized Histogram");
 
   // Normalizing the Histogram by scaling by 1 / the integral and taking width into account
   norm->Scale(1. / norm->Integral(), "width");
 
   // Drawing everything
   TCanvas *c1 = new TCanvas("c1", "Histogram Normalization", 700, 900);
   c1->Divide(1, 2);
 
   c1->cd(1);
   orig->Draw();
   c1->cd(2);
   norm->Draw();
}