void tz()
{
   TRandom3 *ran = new TRandom3(0);
   TH1* h1 = new TH1F("h1","gaussian, weighted", 100, -3., 3.);
   double x, weight;
   for (int i=1; i<=10000; i++) {
      x      = ran->Rndm()*6-3;
      weight = 1/sqrt(2*3.14159)*exp(-1/2*pow(x,2));
      h1->Fill(x, weight);
   }
   h1->Draw();
}