void merge_T(string filelist="inputfile.list")
{
  ifstream fin(filelist.c_str());
  //  TChain T("ntp_cluster");
  TChain T("T");
  string filename;
  while (fin >> filename)
    {
      T.AddFile(filename.c_str());
    }
  T.Merge("merged_dump_jpsi_vertex_eval.root");
}