root> TFile *f = new TFile("zuu307.root")
root> f->ls()
TFile**         zuu307.root
 TFile*         zuu307.root
  KEY: TTree    MUON;1  MUON    
root> Muon->MakeClass("DeltaEtaProducer")

then make changes to DeltaEtaProducer.h and .c

#define DeltaEtaProducer_cxx
#include "DeltaEtaProducer.h"
 
void DeltaEtaProducer::Loop()
{
//   In a Root session, you can do:
//      Root > .L DeltaEtaProducer.C
//      Root > DeltaEtaProducer t
//      Root > t.GetEntry(12); // Fill t data members with entry number 12
//      Root > t.Show();       // Show values of entry 12
//      Root > t.Show(16);     // Read and show values of entry 16
//      Root > t.Loop();       // Loop on all entries
//
 
//     This is the loop skeleton
//       To read only selected branches, Insert statements like:
// METHOD1:
//    fTree->SetBranchStatus("*",0);  // disable all branches
//    fTree->SetBranchStatus("branchname",1);  // activate branchname
// METHOD2: replace line
//    fTree->GetEntry(i);  // read all branches
//by  b_branchname->GetEntry(i); //read only this branch
   if (fTree == 0) return;                                                  
  Float_t deltaEta[50];
  TBranch *deltaEtaB = fTree->Branch("deltaEtaB", &deltaEta,
                        "deltaEta[Nmuonid]/F");
 
   Int_t nentries = Int_t(fTree->GetEntries());
 
   Int_t nbytes = 0, nb = 0;
   Float_t temp;
   for (Int_t i=0; i<nentries;i++) {
      if (LoadTree(i) < 0) break;
      nb = fTree->GetEntry(i);   nbytes += nb;
 
// the following lines are added to process DeltaEta between segment and MC
     for (Int_t j=0; j<Muonid_Nmuonid; j++) {
        deltaEta[j] = 99.0;
 
        for (Int_t k=0; k<MuoMC_Nmmc; k++) {
           temp = Muonid_Ideta[j]-MuoMC_mmceta[k];
           if (abs(temp)<abs(deltaEta[j])) deltaEta[j]=temp;
        }
     }
     cout << "deltaEta["<<j<<"]="<<deltaEta[j]<<endl;
     deltaEtaB->Fill();
   }
   fTree->Write();                                                          
}


then enter into root, execute the following

{
TFile file("zuu307.root","update") 
.L DeltaEtaProducer.C 
DeltaEtaProducer deltaeta 
deltaeta->Loop(); 
}