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update basic analysis example in README files

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1Quick start with Delphes
2========================
3
4Commands to get the code:
5
6   wget http://cp3.irmp.ucl.ac.be/downloads/Delphes-3.4.2.tar.gz
7
8   tar -zxf Delphes-3.4.2.tar.gz
9
10Commands to compile the code:
11
12   cd Delphes-3.4.2
13
14   make
15
16Finally, we can run Delphes:
17
18   ./DelphesHepMC
19
20Command line parameters:
21
22   ./DelphesHepMC config_file output_file [input_file(s)]
23     config_file - configuration file in Tcl format
24     output_file - output file in ROOT format,
25     input_file(s) - input file(s) in HepMC format,
26     with no input_file, or when input_file is -, read standard input.
27
28Let's simulate some Z->ee events:
29
30   wget http://cp3.irmp.ucl.ac.be/downloads/z_ee.hep.gz
31   gunzip z_ee.hep.gz
32   ./DelphesSTDHEP cards/delphes_card_CMS.tcl delphes_output.root z_ee.hep
33
34or
35
36   curl -s http://cp3.irmp.ucl.ac.be/downloads/z_ee.hep.gz | gunzip | ./DelphesSTDHEP cards/delphes_card_CMS.tcl delphes_output.root
37
38For more detailed documentation, please visit
39
40https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook
41
42Configure Delphes on lxplus.cern.ch
43====================================
44
45git clone git://github.com/delphes/delphes.git Delphes
46
47cd Delphes
48
49source  /afs/cern.ch/sw/lcg/external/gcc/4.9.3/x86_64-slc6/setup.sh
50
51source /afs/cern.ch/sw/lcg/app/releases/ROOT/6.06.00/x86_64-slc6-gcc49-opt/root/bin/thisroot.sh
52
53make
54
55
56Simple analysis using TTree::Draw
57=================================
58
59Now we can start ROOT and look at the data stored in the output ROOT file.
60
61Start ROOT and load Delphes shared library:
62
63   root -l
64   gSystem->Load("libDelphes");
65
66Open ROOT file and do some basic analysis using Draw or TBrowser:
67
68   TFile *f = TFile::Open("delphes_output.root");
69   f->Get("Delphes")->Draw("Electron.PT");
70   TBrowser browser;
71
72Note 1: Delphes - tree name, it can be learned e.g. from TBrowser
73
74Note 2: Electron - branch name; PT - variable (leaf) of this branch
75
76Complete description of all branches can be found in
77
78   doc/RootTreeDescription.html
79
80This information is also available at
81
82   https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook/RootTreeDescription
83
84Macro-based analysis
85====================
86
87Analysis macro consists of histogram booking, event loop (histogram filling),
88histogram display.
89
90Start ROOT and load Delphes shared library:
91
92   root -l
93   gSystem->Load("libDelphes");
94
95Basic analysis macro:
96
97{
98  // Create chain of root trees
99  TChain chain("Delphes");
100  chain.Add("delphes_output.root");
101 
102  // Create object of class ExRootTreeReader
103  ExRootTreeReader *treeReader = new ExRootTreeReader(&chain);
104  Long64_t numberOfEntries = treeReader->GetEntries();
105 
106  // Get pointers to branches used in this analysis
107  TClonesArray *branchElectron = treeReader->UseBranch("Electron");
108
109  // Book histograms
110  TH1 *histElectronPT = new TH1F("electron pt", "electron P_{T}", 50, 0.0, 100.0);
111
112  // Loop over all events
113  for(Int_t entry = 0; entry < numberOfEntries; ++entry)
114  {
115
116    // Load selected branches with data from specified event
117    treeReader->ReadEntry(entry);
118 
119    // If event contains at least 1 electron
120    if(branchElectron->GetEntries() > 0)
121    {
122      // Take first electron
123      Electron *electron = (Electron*) branchElectron->At(0);
124     
125      // Plot electron transverse momentum
126      histElectronPT->Fill(electron->PT);
127     
128      // Print electron transverse momentum
129      cout << electron->PT << endl;
130    }
131
132  }
133
134  // Show resulting histograms
135  histElectronPT->Draw();
136}
137
138
139More advanced macro-based analysis
140==================================
141
142The 'examples' directory contains ROOT macros Example1.C, Example2.C and Example3.C.
143
144Here are the commands to run these ROOT macros:
145
146   root -l
147   .X examples/Example1.C("delphes_output.root");
148
149or
150
151   root -l examples/Example1.C'("delphes_output.root")'
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