1. Introduction to “ROOT”
Harinder Singh Bawa
California State University Fresno

2. Outline Revision of Linux environment (First two weeks)
Introduction to CERN ROOT
Installation of CERN ROOT
Browsing ROOT
Dr. Harinder Bawa
1/25/2018

3. Before we Proceed: Week2: scp command
Exercise: Transfer a file from your computer to lxplus account.
Log-in to lxplus and move it to /tmp/username
Transfer a file from /tmp/username to your current working dir.
=> Probably not clear: You need to exit from lxplus and then do last point.
Sol:
scp file.txt (. Or ~/. Means it transfers file to home dir)
ssh > mv file.txt /tmp/bawa/ Exit
scp .
Dr. Harinder Bawa
1/25/2018

4. Shells The shells is a part of the interface for control of linux
There are a number of options, the two most common are:
tc (or c) shell (tcsh)
bourne shell (bash)
Change your shell with chsh
Pick a shell and stick to it, but can be useful for a new account somewhere.
Dr. Harinder Bawa
1/25/2018

5. Environment variables
Much of your linux environment is set by environment variables
These are access via the $sign
eg $HOST
To view your environment use env
Prints out all your environment variables
Use echo to view an individual one
Echo $HOST
Dr. Harinder Bawa
1/25/2018

6. Setting environment variables
You can set your environment variables using
setenv(tc shell)
setenv ROOTSYS /user/local/root
export (bash shell)
export ROOTSYS=/user/local/root
This creates the variable if it doesn’t already exist or updates if it does
Typically the environment variables you set yourself will be to tell programs where to find things.
Dr. Harinder Bawa
1/25/2018

7. Your PATH Your path is an environment variable
$PATH (check by echo $PATH)
It contains all the directories that your OS will look in to find the programs you want to run
The path should contain “.” to ensure that you don’t need to specify it while running local program
Entries are separated by “:”
Update your path with
setenv PATH /newdir:$PATH
Dr. Harinder Bawa
1/25/2018

8. Introduction to ROOT
Dr. Harinder Bawa
1/25/2018

9. What is ROOT? ROOT is an object oriented framework
It has a C/C++ interpreter (CINT) and C/C++ compiler (ACLIC)
ROOT is used extensively in High Energy Physics for “data analysis”
Reading and writing data files
Calculations to produce plots, numbers and fits.
WHY ROOT ?
It can handle large files (in GB) containing N-tuples and Histograms
Multiplatform software
Its based on widely known programming language C++
Its free
Dr. Harinder Bawa
1/25/2018

10. Dr. Harinder Bawa
1/25/2018

11. ROOT and C++
As with everything in this course there is good documentation on the WEB
In the case of ROOT there is one specific place. ‰ „
This is the place to download root from should you need it. „
There is lots of documentation and examples. „
Few examples are in $ROOTSYS/tutorial
Dr. Harinder Bawa
1/25/2018

12. Object Oriented COncepts
Class: the description of a “thing” in the system
Object: instance of a class
Methods: functions for a class
Members: a “has a” relationship to the class.
• Inheritance: an “is a” relationship to the class.
Dr. Harinder Bawa
1/25/2018

13. ROOT Installation
Installation of Root is little tricky. One need to follow exact instructions but not guaranteed(Depends upon version of ROOT and Ubuntu(Linux))
Before we start ROOT Installation, we need to install pre-requisite and make sure it installs that !
Dr. Harinder Bawa
1/25/2018

14. From ROOT Webpage:
Use sudo apt-get install _package_ or use the graphical "Synaptic Package Manager" program. Required packages: sudo apt-get install git dpkg-dev cmake g++ gcc binutils libx11-dev libxpm-dev \ libxft-dev libxext-dev Optional packages: sudo apt-get install gfortran libssl-dev libpcre3-dev \ xlibmesa-glu-dev libglew1.5-dev libftgl-dev \ libmysqlclient-dev libfftw3-dev libcfitsio-dev \ graphviz-dev libavahi-compat-libdnssd-dev \ libldap2-dev python-dev libxml2-dev libkrb5-dev \ libgsl0-dev libqt4-dev
Dr. Harinder Bawa
1/25/2018

15. Dr. Harinder Bawa
1/25/2018

16. Download ROOT in mainly 2 ways
Sources from released versions:
ROOT's sources can be downloaded for each of the releases and unpacked with
$ wget
$ tar -zxf root_<version>.source.tar.gz
* Source: *
Dr. Harinder Bawa
1/25/2018

17. Using GIT Repository Direct Git repository access:
The purpose of Git is to manage a project, or a set of files, as they change over time.Git stores this information in a data structure called a repository
Direct Git repository access:
The main advantages of using the trunk are:
You get the most recent features
You can easily benefit from bug fixes should you find one
To fix or extend ROOT you can change ROOT's sources yourself and send the changes (git diff) as feedback
The entire ROOT source can be obtained from our public Git repository:
$ git clone
Dr. Harinder Bawa
1/25/2018

18. Following steps will work on all systems
Next we will move to the directory where we will install ROOT:
$ cd /usr/local/ (Recommended)
To download the ROOT files run the following command:
$ sudo git clone
Next we will change the ownership of the folder root with:
$ sudo chown -R "username“:”groupname” root
Or command line magic
$sudo chown -R $(whoami):$(id -g -n $(whoami)) root
Dr. Harinder Bawa
1/25/2018

19. Sometime Life is not so easy :
Dr. Harinder Bawa
1/25/2018

20. Building ROOT:
cd root ./configure --all
Dr. Harinder Bawa
1/25/2018

21. Building ROOT:
make
Dr. Harinder Bawa
1/25/2018

22. Not everytime, We are lucky
Root we downloaded using “git” check out the latest version of root.
Sometime, Ubuntu/linux is old enough to be compatible with libraries. For eg : cmake needs to be higher than 3.8 but Ubuntu have 2.8
One can choose little older version(specific tag) of ROOT
$ cd root
$ git tag -l
$ git checkout -b v v
Dr. Harinder Bawa
1/25/2018

23. Dr. Harinder Bawa
1/25/2018

24. Env. Variables
Dr. Harinder Bawa
1/25/2018

25. Env. Variables
New SHELL
Dr. Harinder Bawa
1/25/2018

26. Setting up ROOT export $ROOTSYS=/usr/local/root (Typical path)
You need to have the environment variable ROOTSYS set to the root install directory.
export $ROOTSYS=/usr/local/root (Typical path)
Set root in our PATH
export PATH=$PATH:$ROOTSYS/bin
Also need to use LD_LIBRARY_PATH
This tells programs where to look for libraries
export LD_LIBRARY_PATH=$ROOTSYS/lib:$LD_LIBRARY_PATH
You may define your root settings in ~/.rootlogon.C
History of all commands are stored in ~/.root_hist
Dr. Harinder Bawa
1/25/2018

27. Put permanently in shell(bash)
Dr. Harinder Bawa
1/25/2018

28. Dr. Harinder Bawa
1/25/2018

29. The Framework Organization
Dr. Harinder Bawa
1/25/2018

30. Launching and Quiting ROOT
To launch root: simply root
You should see a splash screen appear, and then root start up in your terminal
root –l (without logo)
root –b(without browser) *Used in running root remotely (using ssh)
To quit root, simply type “.q”
Dr. Harinder Bawa
1/25/2018

31. User Interfaces
Dr. Harinder Bawa
1/25/2018

32. Setup ROOT IN ATLAS
Dr. Harinder Bawa
1/25/2018

33. Setup ROOT IN ATLAS
Dr. Harinder Bawa
1/25/2018

34. GUI: Browsing a file To easily browse a file we use TBrowser
Command : TBrowser b
This makes a TBrowser object called b and then you can quickly look into the contents of the rootfile by clicking the contents.(can be histograms/tree etc)
Ex: open following rootfile in root and look whats inside _ tree.root
Dr. Harinder Bawa
1/25/2018

35. Displaying a Histogram
Open the root file
Browse the file
Display the histograms
The Canvas
Divide Canvas
Dr. Harinder Bawa
1/25/2018

36. Basic Navigation by Clicking
Dr. Harinder Bawa
1/25/2018

37. Draw Panel
Dr. Harinder Bawa
1/25/2018

38. FIT panel
Dr. Harinder Bawa
1/25/2018

39. Adding object to Editor
Adding Arrow
Adding Text
Dr. Harinder Bawa
1/25/2018

40. Modifying the statbox
Dr. Harinder Bawa
1/25/2018

41. Modifying the statbox The Canvas in the Browser
• Setting the (7) statistics options
– default = 1111
If I use: then
Dr. Harinder Bawa
1/25/2018

42. Range of Histogram
Dr. Harinder Bawa
1/25/2018

43. HW Exercise-1(50marks)
Download: _ tree.root
a) Open a ROOT Browser and search for a rootfile & Open tree named “outTree” & Plot following variables and save as pdf files.
njets - Save as njets.pdf Marks:10
Mjj- Save as Invariant Mass Marks:10
yStar- Save as ystar.pdf Marks:10
yBoost- Save as yBoost.pdf Marks:10
b) Open a canvas, Divide into 4 parts as (2x2) and draw above 4 plots and save as pdf file named “Canvas.pdf” Marks:10
Dr. Harinder Bawa
1/25/2018

44. HW Exercise-2 (50 marks)
a) Plot “mjj” in logY scale and color the line of plot as “red”. Save as “mjj_logY.jpg” Marks:10
b) Open a canvas. Plot “mjj” and “m3j” on same canvas superimposed on each other. Put mjj color as “Green” and m3j as “Blue”. Save as “Superimpose.png” Marks 10
c) Plot “pTjj” and modify StatBox so that it shows Underflow and Overflow bins Marks 10
Teaser: Marks 20
Plot “jet_E” from range GeV. Set Xaxis title as “Jet Energy[GeV]”, Y Axis title as “Events”.
Dr. Harinder Bawa
1/25/2018

45. EXTRA
Dr. Harinder Bawa
1/25/2018

46. Open/Loading a file To load a file , type in root prompt:
Root> TFile f(“file.root”)
This creates a TFile object called f
The object f is attached to the file “file.root”
F is a real object and therfore you can use all of TFile member functions.
f->Close() close the file
f->ls() list the objects in a file
Dr. Harinder Bawa
1/25/2018

47. Data Storage in ROOT
There are a number of ways to store and present data in ROOT:
Graphs
A bit like EXCEL: plot x vs y
Histograms:
Stored as Binned data
Ntuples : Tables
Trees : Extension of ntuples
Dr. Harinder Bawa
1/25/2018