Histogram logarithmic with logarithmic bins

ROOT
1

Hi,
I have a code to simulate data of astroparticles, i´m using a logarithmic scale without troubles but i need to implement a logarithmic bin, because a need to see the improbable data, i appreciate your help in this case.
this is the code:

#include <iostream>
#include <fstream>
#include <iostream>
#include <string>
#include <string.h>
#include <sstream>
#include <stdlib.h>
#include <math.h>
#include <sstream>
#include<time.h>

using namespace std;

int potencial()
{
  
  
  //declaracion de variables
  
  long double N=0;
  cout << "Introduzca el numero de variables aleatorias a generar: " << "\n";
  cin  >> N;
  
  long double E_0=0;
  cout << "Introduzca el valor inicial de energia (MeV): " << "\n";
  cin >> E_0;
  
  long double E_m=0;
  cout << "Introduzca el valor maximo de energia(TeV): " << "\n";
  cin >> E_m;
  
  long double alpha=0;
  cout << "Introduzca el valor de alpha: " << "\n";
  cin >> alpha;
  
  E_0= E_0 * 1e6; // MeV
  E_m= E_m * 1e12; // TeV
  
  TH1D* potencial = new TH1D("potencial", "Histograma Potencial de Energias", 100000.,100000.,1000000000.);//(”nombre",”Titutlo”,xBins,lowxbin, upxbin);
  
  potencial->GetXaxis()->SetTitle("MeV");
  potencial->GetYaxis()->SetTitle("frecuencia");
  
  long double  num=0 ;
  long int  i=0, j=0;
  
  
  srand(time(NULL)); //semilla que usa la hora del ordenador para generar numeros aleatorios
  
  for( i = 0; i < N; i++){
    
    num =  rand() % (10000);//numeros aleatorios entre 0 y 1 con 4 decimales
    num = num / 10000;
    
    num = exp(log(( pow(E_m,(1-alpha))-pow(E_0,(1-alpha)) ) * num  + pow(E_0,(1-alpha)))/(1-alpha));
    
    potencial->Fill( (num) );
    
  }
    potencial->Draw();
  // gStyle->SetOptLogx();
  gPad->SetLogx();
  gPad->SetLogy();          
  return 0;
  
}

Luis Hernández
University Central of Venezuela
Science Faculty
Hernandez.y.luis.a@gmail.com
luis.hernandez.y@ucv.ve

2

Search for “variable bin size” in the TH1 class description.

3

Better use this version of the class description:
root.cern.ch/doc/master/classTH1.html

4

thanks, but this can not solve my problem yet, may you help me with an example?

5

The constructor we pointed to you allows to defined the bins limits as you wish using an array. You simply have to fill the array with limits distributed according to a log scale.

6

so, can i put the TH1 into a loop ?

for()
{
TH1D* potencial = new TH1D(“potencial”, “Histograma Potencial de Energias”, 100000.,100000.,1000000000.)

}

something like that but using a variable in the number of bins?

7 
TH1D* potencial = new TH1D("potencial", "Histograma Potencial de Energias", 100000.,100000.,1000000000.)

If you create the histogram this way it will not be a variable bin size one.(also note that there is a type error for the number of bins, it should be an integer).

The variable bin size constructor is:

root.cern.ch/doc/master/classTH … 75b6c7aa5a