jets.C

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// script illustrating the use of a Tree using the JetEvent class.
// The JetEvent class has several collections (TClonesArray)
// and other collections (TRefArray) referencing objects
// in the TClonesArrays.
// The JetEvent class is in $ROOTSYS/tutorials/JetEvent.h,cxx
// to execute the script, do
// .x jets.C
//
//Author: Rene Brun
      
void write(Int_t nev=100) {
   //write nev Jet events
   TFile f("JetEvent.root","recreate");
   TTree *T = new TTree("T","Event example with Jets");
   JetEvent *event = new JetEvent;
   T->Branch("event","JetEvent",&event,8000,2);
   
   for (Int_t ev=0;ev<nev;ev++) {
      event->Build();
      T->Fill();
   }
   
   T->Print();
   T->Write();
}

void read() {
  //read the JetEvent file
  TFile f("JetEvent.root");
  TTree *T = (TTree*)f.Get("T");
  JetEvent *event = 0;
  T->SetBranchAddress("event", &event);
  Int_t nentries = (Int_t)T->GetEntries();
  
  for (Int_t ev=0;ev<nentries;ev++) {
      T->GetEntry(ev);
      if (ev) continue; //dump first event only
      cout << " Event: "<< ev
           << "  Jets: " << event->GetNjet()
           << "  Tracks: " << event->GetNtrack()
           << "  Hits A: " << event->GetNhitA()
           << "  Hits B: " << event->GetNhitB() << endl;
  }
}

void pileup(Int_t nev=200) {
  //make nev pilepup events, each build with LOOPMAX events selected
  //randomly among the nentries
  TFile f("JetEvent.root");
  TTree *T = (TTree*)f.Get("T");
  Int_t nentries = (Int_t)T->GetEntries();
  
  const Int_t LOOPMAX=10;
  JetEvent *events[LOOPMAX];
  Int_t loop;
  for (loop=0;loop<LOOPMAX;loop++) events[loop] = 0;
  for (Int_t ev=0;ev<nev;ev++) {
      if (ev%10 == 0) printf("building pileup: %d\n",ev);
      for (loop=0;loop<LOOPMAX;loop++) {
         Int_t rev = gRandom->Uniform(LOOPMAX);
         T->SetBranchAddress("event", &events[loop]);
         T->GetEntry(rev);
      }
  }
}

void jets(Int_t nev=100, Int_t npileup=200) {
   gSystem->Load("libPhysics");
   gROOT->ProcessLine(".L $ROOTSYS/tutorials/tree/JetEvent.cxx+");
   write(nev);
   read();
   pileup(npileup);
}

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