void combine_rootFiles(){
  TObjArray Hlist(0); // create an array of Histograms

  //auto file = new TFile("/cvmfs/atlas.cern.ch/repo/sw/database/GroupData/SCT_Digitization/SCT_InducedChargedModel.root");
  auto file = new TFile("SCT_InducedChargedModel.root");
  TIter next(file->GetListOfKeys());
  TKey *key;
  cout<<"----- original  files ---------"<<endl;
  file->ls();

  while ((key=(TKey*)next())){
    auto h1 =file->Get(Form("%s",key->GetName()));
//     h1->SetName(Form("%s",key->GetName()));
    Hlist.Add(h1);
  }

  for (int VD=270; VD<=420; VD+=30){
  auto f = new TFile(Form("FEM_M%d_0.root",VD));
  auto Ex = (TH1F*)f->Get(Form("Ex_FEM_M%d_0",VD));
  auto Ey = (TH1F*)f->Get(Form("Ey_FEM_M%d_0",VD));
  Hlist.Add(Ex);
  Hlist.Add(Ey);
  }

  TFile fg("SCT_InducedChargedModel_added.root","recreate");
  Hlist.Write();
  fg.ls();
  return;

}