[[snowmass2013:montecarlo| <<back]]

==== How to analyze in C++ ====

This example shows how to run a C+= program over all Delphes ROOT files located in  a certain directory, fill histograms (pT and jet mass) and save them in an output ROOT file.

Look at the workbook of Delphes3 [[https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook| Delphes3 workbook]].
To get started, install Delphes. You  should see the library "libDelphes.so".  The you can browser the ROOT tree as:

<code C>
gSystem->Load("libDelphes");
TFile::Open("delphes_output.root");
Delphes->Draw("Electron.PT");
TBrowser browser;
</code>


==== Advanced C++ example  ====

This assumes that Delphes3 is already installed. You have the directory "Delphes3" with the shared file "libDelphes.so" inside.

Get the analysis file: {{:snowmass2013:antup.tgz|}}

<code bash>
tar -zvxf antup.tgz
cd antup
</code>

So you will see 2 directories:
<code bash>
delphes3
antup
</code>


Now go to the directory "antup"  and link the existing  Delphes3 installation:

<code bash>
ln -s  ../Delphes3  delphes
</code>

In my case, it will look as:

<code bash>
analysis.h
A_RUN_TEST
data.in
delphes -> ../Delphes3/
main.cxx
Make_input
out
</code>

Check that you see the shared Delphes3 file

<code bash>
ls -l delphes/*so
</code>

You should see "delphes/libDelphes.so" 


The main file which fills histograms is "main.cxx". It fills some jet variables and save histograms in the ROOT file in "/out" directory.

To run the code, run "./A_RUN_TEST" which loops over the existing ROOT files. 
But before you do this, you will need to set "DATA_DIR" variable inside "A_RUN_TEST" to navigate to the directory with your "ROOT" files.

==== How to analyze in PyROOT ====

If ROOT was compiled using "python" option, you can use PyROOT to loop over events. Here is a small example to plot transverse moment of electrons (based on the original code of Peter Onyisi, with some modifications, see
[[https://indico.cern.ch/getFile.py/access?contribId=5&resId=0&materialId=slides&confId=255032| his talk]]):

<code python test.py>
#!/usr/bin/env python
# Based on P.Onyisi example
import sys,os,string
if len(sys.argv)<2:
    print "Usage: python test.py file.root"
    print "Exit.."
    sys.exit()
from ROOT import *
TH1D.SetDefaultSumw2()
gSystem.Load('libDelphes.so')

f=TFile(sys.argv[1])
t=f.Delphes # extract the tree
h=TH1D('ele','Electron #eta',8,-4,4) # initialize a histogram
c1=TCanvas() # build a canvas

n=0
for e in t:   # loop over all events
  if n%100==0: print "Event=",n
  n=n+1
  for electron in e.Electron: # loop over all electrons
     h.Fill(electron.Eta)
h.Draw()
c1.Print('electron.pdf')
if (raw_input("Press any key to exit") != "-9999"):
    c1.Close(); sys.exit(1);
</code>

Run this code as: 
<code>
python test.py file.root
</code>

You will see this image:
{{:snowmass2013:screenshot_from_2013-05-31_21_55_04.png?200|}}

====How to analyze in Java====

MC truth information and most of ROOT files with Delphes outputs
 are stored in the PROMC file format which can be analyzed on any platform.
Read this [[snowmass2013:analyse_d36_promc| this section]].

 --- //[[chekanov@anl.gov|Sergei Chekanov]] 2013/03/13 10:23//