Introduction to ROOT. Sebastian Fleischmann. 06th March 2012 Terascale Introductory School PHYSICS AT THE. University of Wuppertal TERA SCALE SCALE

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1 to ROOT University of Wuppertal 06th March 2012 Terascale Introductory School

2 Basic ROOT classes 4 Interlude: 5 in ROOT 6 es and legends 7 Graphical user interface 8 ROOT trees 9 Appendix: s

3 33 ROOT is an analysis software widely used in particle physics with three main applications Graphics/Plotting Various 1-dim to 3-dim plot styles Also 3D graphics support Data analysis Math library Additional analysis libraries, e.g. RooStats (statistics tools) and TMVA (neural networks, boosted decision trees, etc), see Terascale statistics school Data storage ROOT has optimised data structures for event based data allows to store arbitrary C++ classes

4 44 Documentation During this tutorial and your work you will often need the ROOT documentation User s guide: content/users-guide Reference of all ROOT classes: reference-guide ClassIndex.html Exercises for this tutorial: ~fleischm/lehre/root/tutorial.html

5 55 My first > ini ROOT532_64 # at NAF: ini ROOT53200 > root ******************************************* * * * W E L C O M E to R O O T * * * * Version 5.32/00 2 December 2011 * * * * You are welcome to visit our Web site * * * * * ******************************************* ROOT 5.32/00 (tags/v @42375, Dec , 12:42:25 on l CINT/ROOT C/C++ Interpreter version , July 2, 2010 Type? for help. Commands must be C++ statements. Enclose multiple statements between. root [0]

6 66 My first The C interpreter CINT ROOT includes a C interpreter (CINT) root [0] (const double) e+00 root [1] for (unsigned int i=0; i!=3; i++) { \ > std::cout«i«std::endl;} root [2] Allows to perform simple calculations interactively How to get out of ROOT: root [2].q >

7 77 My first Executing macros CINT commands can also be executed from a macro file: test1.c 1 void test1(){ 2 for (unsigned int i=0; i<3; i++) { 3 std::cout<<i<<std::endl; 4 } 5 } > root -l test1.c root [0] Processing test1.c root [1].q root -l suppresses the ROOT welcome screen

8 My first Loading and compiling macros 88 Helmholtz Alliance You can load macros and execute functions defined inside: > root -l root [0].L test1.c root [1] test1() root [2].q You can also compile macros to ensure correct syntax: > root -l root [0].L test1.c+ Info in <TUnixSystem::ACLiC>: creating shared library./test1 In file included from./test1_c_aclic_dict.h:33, from./test1_c_aclic_dict.cxx:16:./test1.c: In function âvoid test1()â:./test1.c:3: error: âcoutâ is not a member of âstdâ./test1.c:3: error: âendlâ is not a member of âstdâ g++:./test1_c_aclic_dict.o: Datei oder Verzeichnis nicht gef Error in <ACLiC>: Compilation failed! root [1]

9 99 My first Loading and compiling macros Ok, so fix the code: 1 #include <iostream> 2 void test1(){ 3 for (unsigned int i=0; i<3; i++) { 4 std::cout<<i<<std::endl; 5 } 6 } root [0].L test1.c+ Info in <TUnixSystem::ACLiC>: creating shared library./test1 root [1] test1() root [2] Compiling makes execution faster and helps to find syntax errors

10 Classes and functions in the TMath namespace The TMath namespace (use with #include "TMath.h") contains ROOT implementations of various mathematical functions and constants, eg constants: TMath::Pi(), TMath::C() functions: TMath::Log2(x), TMath::Poisson(x, par) 10 10

11 TLorentzVector TLorentzVector is a ROOT class for a physical 4-vector constructor: TLorentzVector myvec(px, py, pz, e); setting components: myvec.setxyzm(px, py, pz, m); myvec.setptetaphie(pt, eta, phi, e); and several others, see root/html/tlorentzvector.html getting p T, η: myvec.pt(); myvec.eta(); arithmetic operations are possible: TLorentzVector myvec3 = myvec1+myvec1; TLorentzVector myvec3 = 5. * myvec1; as well as calculations of angles between spatial components: double deltaphi = myvec1.deltaphi(myvec2); 11 11

12 Exercise 1 Please try to work through exercise 1 now ~fleischm/lehre/root/tutorial.html 12 12

13 Interlude Memory management in ROOT and pointers Helmholtz Alliance are used in C++ to create memory resistant (permanent, non-local) objects Distinguish pointer and the actual object Creating an object of TLorentzVector and obtaining a pointer to it with new: 1 // creating a TLorentzVector in memory 2 // and get pointer to it: 3 TLorentzVector* tlvpointer = 4 new TLorentzVector(px, py, pz, e); 5 // access functions of the object that is pointed to: 6 double pt = tlvpointer->pt(); 7 // remove the object from memory 8 delete tlvpointer; 9 tlvpointer = 0; compared to 1 // creating a TLorentzVector locally: 2 TLorentzVector tlv(px, py, pz, e); 3 // access functions of the object: 4 double pt = tlv.pt(); 5 // object automatically removed when out of scope

14 Interlude Memory management in ROOT and pointers Many ROOT objects, like histograms, trees, canvases (we will use those in the following), are created with a name, i.e. a string to identify them ROOT holds a list of these objects and will automatically delete them, when ROOT is terminated You should usually created named objects with unique names, i.e. do not reuse an existing name 14 14

15 in ROOT Many data in high energy physics are presented as histograms, therefore the 1-dimensional histogram class TH1 is one of the basic classes in ROOT. 1 #include "TH1.h" Entries [GeV] E Jet 2 // create 1dim histogram with 100 bins from 0 to 1000: 3 TH1F* hist = new TH1F 4 ("histname", "title;x label;y label", 100, 0., 1000.); 5 // Fill entries: 6 hist->fill(30.); 7 hist->fill(50.); 8 // draw the histogram: 9 hist->draw(); 15 15

16 in ROOT I Not only 1-dimensional histograms (TH1), but also 2-dim (TH2) and 3-dim (TH3) histograms are supported. I Bin entries can be integer (TH1I) or floating point numbers (TH1F). 16

17 Exercise 2 Please try to work through exercise 2 now ~fleischm/lehre/root/tutorial.html 17 17

18 es and legends in ROOT ROOT distinguishes between the histogram and the canvas on which the histogram is drawn (the canvas may even be divided in pads, but we ignore this...) One can also draw several histograms into the same coordinate system If more than one histogram is drawn one should add a legend 18 18

19 Exercise 3 Please try to work through exercise 3 now ~fleischm/lehre/root/tutorial.html 19 19

20 Graphical user interface () The Editor The is rudimentary in ROOT, but sufficient to adjust many parameters Enable the editor and toolbar on a canvas via the window s menu Right-click on an object opens its context menu 20 20

21 Graphical user interface TBrowser The TBrowser allows to browse files and draw their contents You can open it with new TBrowser; Note: There is a new and an old TBrowser, if your TBrowser looks differently you are most likely using an old ROOT version 21 21

22 Exercise 4 Please try to work through exercise 4 now ~fleischm/lehre/root/tutorial.html 22 22

23 Data storage in ROOT: ROOT can store data in a TTree TTree has entries (e.g. collision events) each with identical data structure One entry at a time can be loaded from the TTree into memory B. Bellenot, A. Naumann; CSC09

24 Exercise 5 Please try to work through exercise 5 now ~fleischm/lehre/root/tutorial.html 24 24

25 Appendix Vectors in the Standard Template Library (STL) Helmholtz Alliance s are no vectors in the mathematical sense, like ROOT s TLorentzVector, but containers to store arrays with variable size of other objects. They are templated, i.e. you can create a vector of nearly all classes, e.g. std::vector<float> or std::vector<tlorentzvector>. 1 // creating a vector of floats with size 0: 2 std::vector<float> myfloatvec; 3 // adding an entry with value 100. to the end: 4 myfloatvec.push_back(100.); 5 // accessing the first entry: 6 std::cout << myfloatvec[0] << std::endl; 7 // resizing a vector and setting new entries to 10: 8 myfloatvec.resize(5, 10.); 9 // looping over a vector with iterators: 10 std::vector<float>::iterator iter = myfloatvec.begin(); 11 for (; iter!=myfloatvec.end(); iter++) { 12 std::cout << (*iter) << std::endl; 13 }