tree0.C File Reference

Detailed Description

Simple Event class example

execute as: .x tree0.C++

You have to copy it first to a directory where you have write access! Note that .x tree0.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() marcro 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)
};

//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;
  ClassDef(Event,1)
};

ClassImp(Event)

void tree0() {
  // create a TTree
  TTree *tree = new TTree("tree","treelibrated tree");
  Event *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) cout<<"Processing event "<<iev<<"..."<<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
  TCanvas *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

  cout<<endl;
  cout<<"You can now examine the structure of your tree in the TreeViewer"<<endl;
  cout<<endl;
}

Author

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

Definition in file tree0.C.