Hello,

I have recently noticed that TRandom3( ) gives repeating numbers. By this, I mean that when I am trying to generate data for a given probability distribution function, for a small number of events, such as 4e6, I get about 150 instances of exactly the same random number being generated (meaning there are 150 pairs of numbers). The exact values of these numbers are subject to change for different seeds, but nevertheless I consistently see about 150 instances of “repeating numbers”. My first guess was that this was a precision issue, but writing out at least 30 significant figures revealed these “repeating numbers” were identical to these large number of decimal places. I wanted to know if there is any mistake in my code. The code is as follows. The first function generates random numbers under the given distribution and the second function counts how many number are repeated.

Thanks,

Mojtaba.

```
#define _USE_MATH_DEFINES
#include <cmath>
#include <cstdlib>
#include <fstream>
#include <iostream>
// Root libraries
#include "TRandom3.h"
#include <TFile.h>
#include <TH1D.h>
#include <TTree.h>
#include <fstream>
#include <iostream>
#include <math.h>
#include <string>
#include <iomanip>
#include <vector>
#include <cstdlib>
#include <sstream>
#include <algorithm>
using namespace std;
Double_t w(double x)
{
Double_t E=M_E;
Double_t Pi=M_PI;
Double_t value=(1. - cos(Pi/8. + x/10.)/pow(E,x/500.))/pow(E,x/1000.);
return value;
}
void tmgn() {
cout.precision(24);
Double_t x, y;
TFile *fileout = new TFile("5dfnctn15.root", "RECREATE");
TTree *Tout= new TTree("Tout", "timegen");
Tout->Branch("time",&x,"x/D");
Int_t nBins = 300;
Double_t xMin = 0.0;
Double_t xMax = 1500.0;
gRandom = new TRandom3(0);
//TRandom3 rand(0);
Int_t nEvents = 1e6;
ofstream myconf;
myconf.precision(30);
Int_t i;
myconf.open("5dfnctn15.dat",ios::trunc);
Int_t counter=0;
for (i = 0; i < nEvents; i++) {
Double_t ceiling, test, prob;
ceiling =2.0001;
test = 1.;
prob = 0.;
while (test > prob) {
//x = xMin + (xMax - xMin) * rand.Rndm();
x = xMin + (xMax - xMin) * gRandom->Uniform(1.0);
y = w(x);
prob = (double)y / (double) ceiling;
test = gRandom->Uniform(1.0);
// test = rand.Rndm();
counter+=1;
}
Tout->Fill();
myconf<<x<<endl;
}
fileout->Write();
fileout->Close();
cout<<"Out of"<<" "<<counter<<" "<<"events,"<<" "<<nEvents<<" "<<"were accepted"<<endl;
}
void repeatnum(){
ifstream fin;
fin.open("5dfnctn17.dat");
Double_t number;
Int_t count=0;
vector<Double_t> mtrx;
while(fin >> number){
mtrx.push_back(number);
}
std::sort (mtrx.begin(), mtrx.end());
const Int_t nevents = mtrx.size();
for (Int_t i=0;i<nevents; i++) {
if(mtrx[i+1]==mtrx[i]){
count+=1;
}
}
cout<<"There are"<<" "<<count<<" "<<"repeating numbers"<<endl;
}
```

Repeatpost.C (1.9 KB)

*ROOT Version:* 6.15/01

*Platform:* macosx64

*Compiler:* gcc 4.2.1