[ROOT] ROOT: Speed problem

From: Jan Musinsky (mucha@sunhe.jinr.ru)
Date: Tue Jul 02 2002 - 11:20:55 MEST 

 Hi,
I have met a stupid (maybe) problem.
I use tree to analyze ...:


  UShort_t nchar=0;
  Float_t px[MAX_TRACK];

  TFile *fin = new TFile("oxygen.root","READ");
  if (!(fin.IsOpen())) break;
  TTree *oxy = (TTree*)fin->Get("oxy");

  oxy->SetBranchAddress("nchar",&nchar);
  oxy->SetBranchAddress("px",px);

  UInt_t nevents=oxy->GetEntries();
  for (UInt_t i=0; i<nevents; i++) {
      oxy->GetEntry(i);
      ....
      using nchar
      using px[...]
      ....
   
      for (UInt_t i2=1; i2<500; i2++) {
           UShort_t event2 = (gRandom->Rndm())*nevents;
           if (event2 == i) event2 = (gRandom->Rndm())*nevents;
           oxy->GetEntry(event2);
           ...
           using nchar
           using px[...]
           ....
       } // end i2
   } // end i



The result is that the analysis of the root takes days, days, ..
Can I somehow speed it up ?
Thanks in advance,
Jan

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