{
  // example to generate gaussian MC events using trasformation method
  // first, solve the trasformation equation:
  //  (Integral of Gaus(x', mean, sigma)dx' from -inf to x ) = r
  // one get x = mean - sqrt(2)*sigma*Erf^{-1}(1-2r)

  // define randome number with randome seed 1234 (can be any number) 
  TRandom3 rnd(1234); 
 
  // define a histogram from 0 to 1.5
  TH1D* h1 = new TH1D("h1", "h1", 100,-10,20);

  // define the values of mean and sigma
  double mean = 5;
  double sigma = 3;

  // generate random number 
  for( int i=0; i<10000; i++) {
    //generate random r from 0 to 1
    double r = rnd.Rndm();
    // calculate random variable x
    double x = mean - sqrt(2.0)*sigma*TMath::ErfInverse(1.0-2.0*r);
    // fill it into histogram
    h1->Fill(x);

  }

  // draw h1
  h1->Draw();



  



}