{
  TFile* file = new TFile("test.root","READ");
  TTree* tree = file->Get("vtuple");
  float pt[128];
  tree->SetBranchAddress("ptAK4H1TPJ",&pt);
  TTreeFormula* formula = new TTreeFormula("Selection","ptAK4H1TPJ>0",vtuple) ;
  tree->GetEntry(0);
  cout << "pt[0]: " << pt[0] << " formula returns " << formula->EvalInstance(0) << endl;
  pt[0] = -1;
  cout << "changed pt[0]: " << pt[0] << " formula returns " << formula->EvalInstance(0) << endl;
}