How To Use ROOT - some features - Ann-Cecilie Larsen & Alexander Bürger 15 Januar 2009 OCL group meeting
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How To Use ROOT
-- some features
Ann-Cecilie Larsen & Alexander Bürger
15 Januar 2009
OCL group meeting
What is ROOT?
Object-Oriented framework for
data analysis
data acquisition
...
developed at CERN
implemented in C++
C++ interpreter CINT
allows to run C++ code without compilation
Why C++?
helps with object oriented programming (OOP)
simplifies maintenance of large projects
means
encapsulation (data access control)
inheritance (generalization hierarchy)
polymorphism (different implementation in inheritance tree)
“based” on C
could do OOP in C, BUT
no compiler support, more complicated syntax
far more work, more typing, more errorsClasses 'in Nature'
very general: something
animal
arrow= “is a” “abstract”: does not actually exist
very specific,
fish mammal
not “abstract”, can exist
...
cow dog 'instance' with
specific
property values
Romeo
class: describes set of properties and 'functions'
color of fur, weight, bark(), eat()
object: instance of a class with a specific set of
properties
white fur, 40kgClasses in C++
// derived class definition
a class is a set of class Histogram {
public:
object properties void Fill(float value);
int GetNbins();
virtual float GetBinContent(int bin);
methods/functions protected:
float* GetBins() const { return bins; }
private:
constructor&destructor int nbins; encapsulation
float* bins;
variables };
...
// method definition
objects are instances float Histogram::GetBinContent(int bin)
{
of their class }
return bins[bin];
...
// create an instance
Histogram* h1 = new Histogram(...);
cout GetBinContent(5)Inheritance
arrow=“derived from”
very general: something
TObject
“abstract”: does not actually exist
TVirtualPad something with a name
TNamed
still “abstract”
TCanvas ...
histogram with bins, axes, ...
TH1
not “abstract”, can exist
...
...
a derived class
inherits all methods/functions from the base class
may override some methods
e.g. TObject::Draw is overridden by TH1::DrawDerived Classes
inheritance
a derived class can // derived class definition
class SafeHistogram : public Histogram {
public:
override (replace) float GetBinContent(int bin); // virtual
int GetNbins(); // not virtual
methods/functions };
...
// method definition
polymorphism
add variables and float SafeHistogram::GetBinContent(int bin)
{
methods if( bin>=0 && binSyntactic Sugar -- “Typing help”
a[i][j] // instead of *(*(a + i) + j)
less typing, easier to h1>GetNbins() // instead of (*h1).GetNbins()
read, fewer errors #include
ifstream input_file(“/tmp/plot.dat”);
float x, y;
examples input_file >> x >> y;
// definition: istream& istream::operator>>(float& x);
array access void do_something(int x); // integer argument
void do_something(double x); // double argument
void do_something(string s); // string
stream const char* text = “OCL”;
extraction/insertion do_something(text); // creates temporary
// string object
float f = 15.1;
name overloading do_something(f); // conversion may be tricky!
distinguish functions by
signature (name + types)
implicit type conversionTemplates and the STL
templates // bad:
#define MAX(a,b) ((a>b)?a:b)
MAX(“here”,”there”); // compares pointers
MAX(f(1),f(2)); // calls f three times
“generic classes” // better
template
help avoid preprocessor T& max(T& a, T& b)
{
macros if( a > b )
return a;
else
STL – standard }
return b;
template library
max(f(1),f(2)); // calls f two times
// automatically figures T
max(10, 15.1); // int and double
implements often- template
class vector {
needed things public:
unsigned size() const { ... }
};
examples #include
#include
sorted collections std::map mymap;
coutWhere to Get Help with ROOT?
Homepage: http://root.cern.ch/
documentation
tutorials
user forum
...
ROOT User's Guide (PDF from homepage)
from people using ROOT
MacOS finder: swshareroottutorialsInstalling ROOT on MacOS
easiest with fink
shows i if installed
otherwise install with
fink install root5
in a terminalStarting and Stopping
start: “root”
in a terminal
stop: “.q”Running Scripts
.x mymacro.C .x mymacro.C+ or
interpreted mode .x mymacro.C++
compiled modeScript Example
// CINT automatically uses “using namespace std”, some
“#include”s, ... levdens46Ti SetStyle("Plain"); // no colors/fill areas int j;
gStyle>SetOptTitle(0); // no histogram title rho46file >> j >> energy46[i] >> rho46[i] >> rhoerr46[i];
gStyle>SetOptTitle(1); levdens46TiScript Example (2)
rho44ti>SetMarkerStyle(20);
rho44ti>SetMarkerSize(0.8);
rho44ti>SetMarkerColor(kBlue);
rho44ti>SetLineColor(kBlue);
rho44ti>Draw("P"); // draw as points with line
rho46ti>SetMarkerStyle(24);
rho46ti>SetMarkerSize(0.8);
rho46ti>Draw("P");
// create legend to visualize where the data points belong
TLegend *leg = new TLegend(0.15,0.60,0.6,0.75);
leg.SetBorderSize(0);
leg>AddEntry(rho44ti,"Oslo data, ^{44}Ti (norm. E&B)","P");
leg>AddEntry(rho46ti,"Oslo data, ^{46}Ti (norm. E&B)","P");
leg>Draw();
// add some LaTeX text
TLatex t;
t.SetTextSize(0.05);
t.DrawLatex(/*X=*/1.502,
/*y=*/1.632e+04,
"^{44}Ti and ^{46}Ti level density #rho");
c1>Update(); // actually draw something before “printing” it
c1>Print("example.eps"); // “print” as .eps
c1>Print("example.pdf"); // “print” as .pdf
} // END of scriptYou can also read
