// ===================================================================
//
// Simple example on how to generate random numbers in c++. Please 
// notice that you will need c++ 11. To use it you need gcc 4.7.2 
// that can be invoked by 
//
// scl enable devtoolset-1.1 bash
//
// Also examples using ROOT are given 
//
// ===================================================================


#include <iostream>
#include <iomanip>
#include <string>
#include <map>
#include <random>
#include <cmath>

#include "TH1F.h"
#include "TCanvas.h"
#include "TApplication.h"
#include "TRandom.h" 

int main()
{

  TApplication app("app",0,0);

  // Generate random numbers using c++ library <random> ( since c++ 11)
  // create a random number engine. In this case a simple LCG ( minstd_rand0
  // or Marsenne Twister 19937 generators

  //  std::minstd_rand0 e1 (2.);
    
  std::mt19937 e1 (2.) ;

  // c++ 11 implements several distributions. Generate pseudo random
  // numbers and fill histograms

  std::uniform_real_distribution<double> uniform_dist(1, 6);
  TH1F hunif("uniform","Uniform distribution",100, 0, 10);
  for ( int k = 0 ; k < 10000 ; k++ ) hunif.Fill( uniform_dist(e1) );
  
  std::normal_distribution<> normal_dist(2, 1);
  TH1F hgauss("gauss","Normal distribution",100, -10, 10); 
  for (int n = 0; n < 10000; n++) hgauss.Fill( normal_dist( e1  ) ); 
  
  std::exponential_distribution<> expo_dist(0.5);
  TH1F hexpo("expo","Exponential distribution",100, 0, 20);
  for (int n = 0; n < 10000; n++) hexpo.Fill( expo_dist( e1  ) );

  std::poisson_distribution<> pois_dist(4);
  TH1F hpois("Poisson","Poisson distribution",15, 0, 15);
  for (int n = 0; n < 10000; n++) hpois.Fill( pois_dist( e1  ) ) ;
  
  // show histograms

  TCanvas * can = new TCanvas("distributions","Random numbers generator");
  can->Divide(2,2);
  can->cd(1);

  hunif.Draw();
  can->cd(2);
  hgauss.Draw();

  can->cd(3);
  hexpo.Draw();

  can->cd(4);
  hpois.Draw();

  // Generate random numbers with ROOT. Create a TRandom object and then 
  // call its various methods.ll

  TRandom rand(2.);

  TH1F Rhunif("Uniform(ROOT)","Uniform(ROOT)",100, 0, 10);
  TH1F Rhgaus("gaus(ROOT)","Normal distribution(ROOT)",100, -10, 10);
  TH1F Rhexpo("expo(ROOT)","Exponential distribution(ROOT)",100, 0, 20);
  TH1F Rhpois("Poisson(ROOT)","Poisson distribution(ROOT)",15, 0, 15);

  for (int n = 0; n < 10000; n++) Rhunif.Fill( rand.Uniform(1,6) ) ;
  for (int n = 0; n < 10000; n++) Rhgaus.Fill( rand.Gaus(2,1)    ) ;
  for (int n = 0; n < 10000; n++) Rhexpo.Fill( rand.Exp(0.5)     ) ;
  for (int n = 0; n < 10000; n++) Rhpois.Fill( rand.Poisson(4)   ) ;

  TCanvas * Rcan = new TCanvas("distributions(ROOT)","Random numbers generator(ROOT)");
  Rcan->Divide(2,2);
  Rcan->cd(1);

  Rhunif.Draw();
  Rcan->cd(2);
  Rhgaus.Draw();

  Rcan->cd(3);
  Rhexpo.Draw();

  Rcan->cd(4);
  Rhpois.Draw();

  app.Run();

}