tree103_tree.C

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/// \file
/// \ingroup tutorial_tree
/// \notebook -nodraw
/// Simple Event class example
///
/// execute as: .x tree103_tree.C++
///
///  You have to copy it first to a directory where you have write access!
///  Note that .x tree103_tree.C cannot work with this example
///
/// ### Effect of ClassDef() and ClassImp() macros
///
/// After running this macro create an instance of Det and Event
///
/// ~~~
///   Det d;
///   Event e;
/// ~~~
///
/// now you can see the effect of the  ClassDef() and ClassImp() macros.
/// (for the Det class these commands are commented!)
/// For instance 'e' now knows who it is:
///
/// ~~~
///   cout<<e.Class_Name()<<endl;
/// ~~~
///
/// whereas d does not.
///
/// The methods that are added by the ClassDef()/Imp() macro can be listed with
///
/// ~~~
/// .class
///   .class Event
///   .class Det
/// ~~~
///
/// \macro_code
///
/// \author Heiko.Scheit@mpi-hd.mpg.de
 
#include <TRandom.h>
#include <TTree.h>
#include <TCanvas.h>
#include <TStyle.h>
 
#include <Riostream.h>
 
//class Det : public TObject  {
class Det {  // each detector gives an energy and time signal
public:
   Double_t e; //energy
   Double_t t; //time
 
//   ClassDef(Det,1)
};
 
//ClassImp(Det)
 
//class Event { //TObject is not required by this example
class Event : public TObject {
public:
   Det a; // say there are two detectors (a and b) in the experiment
   Det b;
 
   ClassDefOverride(Event,1)
};
 
ClassImp(Event)
 
void tree103_tree()
{
   // create a TTree
   auto tree = new TTree("tree", "treelibrated tree");
   auto e = new Event;
 
   // create a branch with energy
   tree->Branch("event", &e);
 
   // fill some events with random numbers
   Int_t nevent = 10000;
   for (Int_t iev=0; iev<nevent; iev++) {
      if (iev % 1000 == 0)
         std::cout << "Processing event " << iev << "..." << std::endl;
 
      Float_t ea, eb;
      gRandom->Rannor(ea, eb); // the two energies follow a gaus distribution
      e->a.e = ea;
      e->b.e = eb;
      e->a.t = gRandom->Rndm();  // random
      e->b.t = e->a.t + gRandom->Gaus(0., .1);  // identical to a.t but a gaussian
                                                // 'resolution' was added with sigma .1
      tree->Fill();  // fill the tree with the current event
   }
 
   // start the viewer
   // here you can investigate the structure of your Event class
   tree->StartViewer();
 
   //gROOT->SetStyle("Plain");   // uncomment to set a different style
 
   // now draw some tree variables
   auto c1 = new TCanvas();
   c1->Divide(2, 2);
   c1->cd(1);
   tree->Draw("a.e");  //energy of det a
   tree->Draw("a.e", "3*(-.2<b.e && b.e<.2)", "same");  // same but with condition on energy b; scaled by 3
   c1->cd(2);
   tree->Draw("b.e:a.e", "", "colz");        // one energy against the other
   c1->cd(3);
   tree->Draw("b.t", "", "e");    // time of b with errorbars
   tree->Draw("a.t", "", "same"); // overlay time of detector a
   c1->cd(4);
   tree->Draw("b.t:a.t");       // plot time b again time a
 
   std::cout << std::endl;
   std::cout << "You can now examine the structure of your tree in the TreeViewer" << std::endl;
   std::cout << std::endl;
}