void exemplo_TH2()
    {
      TRandom *r = new TRandom();
      TH2F *h2 = new TH2F("h","Exemplo Th2",50,0,10,50,0,5);
      for(int i = 0;i<2000;i++)
      {
        float x = r->Gaus(5,1);
        float y = r->Gaus(3,0.5);
        h2->Fill(x,y);
      }
      h2->Draw();
    }