tree103_tree.C File Reference

Detailed Description

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() macro

After running this macro create an instance of Det and Event

Det d;
Event e;

now you can see the effect of the ClassDef() macro. (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() macro can be listed with

.class
  .class Event
  .class Det

 
#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)
};
 
//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)
};
 
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;
}
 

Author

Heiko.nosp@m..Sch.nosp@m.eit@m.nosp@m.pi-h.nosp@m.d.mpg.nosp@m..de

Definition in file tree103_tree.C.