void tree113_getval()
{
   // create a simple TTree with 5 branches
   Int_t run, evt;
   Float_t x, y, z;
   auto T = new TTree("T", "test friend trees");
   T->Branch("Run", &run, "Run/I");
   T->Branch("Event", &evt, "Event/I");
   T->Branch("x", &x, "x/F");
   T->Branch("y", &y, "y/F");
   T->Branch("z", &z, "z/F");
   TRandom r;
   for (Int_t i=0; i<10000; i++) {
      if (i < 5000)
         run = 1;
      else
         run = 2;
      evt = i;
      x = r.Gaus(10, 1);
      y = r.Gaus(20, 2);
      z = r.Landau(2, 1);
      T->Fill();
   }

   // Draw with option goff and generate seven variables
   Int_t n = T->Draw("x:y:z:Run:Event:sin(x):cos(x)", "Run==1", "goff");
   printf("The arrays' dimension is %d\n", n);

   // Retrieve variables 0, 5 et 6
   Double_t *vx  = T->GetVal(0);
   Double_t *vxs = T->GetVal(5);
   Double_t *vxc = T->GetVal(6);

   // Create and draw graphs
   auto gs = new TGraph(n, vx, vxs);
   auto gc = new TGraph(n, vx, vxc);
   gs->Draw("ap");
   gc->Draw("p");
}