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Reference Guide
tree2.C
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1/// \file
2/// \ingroup tutorial_tree
3/// \notebook
4/// This example illustrates how to make a Tree from variables or arrays
5/// in a C struct - without a dictionary, by creating the branches for
6/// builtin types (int, float, double) and arrays explicitly.
7/// See tree2a.C for the same example using a class with dictionary
8/// instead of a C-struct.
9///
10/// In this example, we are mapping a C struct to one of the Geant3
11/// common blocks /gctrak/. In the real life, this common will be filled
12/// by Geant3 at each step and only the Tree Fill function should be called.
13/// The example emulates the Geant3 step routines.
14///
15/// to run the example, do:
16/// ~~~
17/// .x tree2.C to execute with the Cling interpreter
18/// .x tree2.C++ to execute with native compiler
19/// ~~~
20/// \macro_code
21///
22/// \author Rene Brun
23
24#include "TFile.h"
25#include "TTree.h"
26#include "TH2.h"
27#include "TRandom.h"
28#include "TCanvas.h"
29#include "TMath.h"
30
31const Int_t MAXMEC = 30;
32
33typedef struct {
34 Float_t vect[7];
35 Float_t getot;
36 Float_t gekin;
37 Float_t vout[7];
38 Int_t nmec;
39 Int_t lmec[MAXMEC];
40 Int_t namec[MAXMEC];
41 Int_t nstep;
42 Int_t pid;
43 Float_t destep;
44 Float_t destel;
45 Float_t safety;
46 Float_t sleng;
47 Float_t step;
49 Float_t sfield;
50 Float_t tofg;
51 Float_t gekrat;
52 Float_t upwght;
53} Gctrak_t;
54
55
56void helixStep(Float_t step, Float_t *vect, Float_t *vout)
57{
58 // extrapolate track in constant field
59 Float_t field = 20; //magnetic field in kilogauss
60 enum Evect {kX,kY,kZ,kPX,kPY,kPZ,kPP};
61 vout[kPP] = vect[kPP];
62 Float_t h4 = field*2.99792e-4;
63 Float_t rho = -h4/vect[kPP];
64 Float_t tet = rho*step;
65 Float_t tsint = tet*tet/6;
66 Float_t sintt = 1 - tsint;
67 Float_t sint = tet*sintt;
68 Float_t cos1t = tet/2;
69 Float_t f1 = step*sintt;
70 Float_t f2 = step*cos1t;
71 Float_t f3 = step*tsint*vect[kPZ];
72 Float_t f4 = -tet*cos1t;
73 Float_t f5 = sint;
74 Float_t f6 = tet*cos1t*vect[kPZ];
75 vout[kX] = vect[kX] + (f1*vect[kPX] - f2*vect[kPY]);
76 vout[kY] = vect[kY] + (f1*vect[kPY] + f2*vect[kPX]);
77 vout[kZ] = vect[kZ] + (f1*vect[kPZ] + f3);
78 vout[kPX] = vect[kPX] + (f4*vect[kPX] - f5*vect[kPY]);
79 vout[kPY] = vect[kPY] + (f4*vect[kPY] + f5*vect[kPX]);
80 vout[kPZ] = vect[kPZ] + (f4*vect[kPZ] + f6);
81}
82
83void tree2w()
84{
85 //create a Tree file tree2.root
86
87 //create the file, the Tree and a few branches with
88 //a subset of gctrak
89 TFile f("tree2.root","recreate");
90 TTree t2("t2","a Tree with data from a fake Geant3");
91 Gctrak_t gstep;
92 t2.Branch("vect",gstep.vect,"vect[7]/F");
93 t2.Branch("getot",&gstep.getot);
94 t2.Branch("gekin",&gstep.gekin);
95 t2.Branch("nmec",&gstep.nmec);
96 t2.Branch("lmec",gstep.lmec,"lmec[nmec]/I");
97 t2.Branch("destep",&gstep.destep);
98 t2.Branch("pid",&gstep.pid);
99
100 //Initialize particle parameters at first point
101 Float_t px,py,pz,p,charge=0;
102 Float_t vout[7];
103 Float_t mass = 0.137;
104 Bool_t newParticle = kTRUE;
105 gstep.step = 0.1;
106 gstep.destep = 0;
107 gstep.nmec = 0;
108 gstep.pid = 0;
109
110 //transport particles
111 for (Int_t i=0;i<10000;i++) {
112 //generate a new particle if necessary
113 if (newParticle) {
114 px = gRandom->Gaus(0,.02);
115 py = gRandom->Gaus(0,.02);
116 pz = gRandom->Gaus(0,.02);
117 p = TMath::Sqrt(px*px+py*py+pz*pz);
118 charge = 1; if (gRandom->Rndm() < 0.5) charge = -1;
119 gstep.pid += 1;
120 gstep.vect[0] = 0;
121 gstep.vect[1] = 0;
122 gstep.vect[2] = 0;
123 gstep.vect[3] = px/p;
124 gstep.vect[4] = py/p;
125 gstep.vect[5] = pz/p;
126 gstep.vect[6] = p*charge;
127 gstep.getot = TMath::Sqrt(p*p + mass*mass);
128 gstep.gekin = gstep.getot - mass;
129 newParticle = kFALSE;
130 }
131
132 // fill the Tree with current step parameters
133 t2.Fill();
134
135 //transport particle in magnetic field
136 helixStep(gstep.step, gstep.vect, vout); //make one step
137
138 //apply energy loss
139 gstep.destep = gstep.step*gRandom->Gaus(0.0002,0.00001);
140 gstep.gekin -= gstep.destep;
141 gstep.getot = gstep.gekin + mass;
142 gstep.vect[6] = charge*TMath::Sqrt(gstep.getot*gstep.getot - mass*mass);
143 gstep.vect[0] = vout[0];
144 gstep.vect[1] = vout[1];
145 gstep.vect[2] = vout[2];
146 gstep.vect[3] = vout[3];
147 gstep.vect[4] = vout[4];
148 gstep.vect[5] = vout[5];
149 gstep.nmec = (Int_t)(5*gRandom->Rndm());
150 for (Int_t l=0;l<gstep.nmec;l++) gstep.lmec[l] = l;
151 if (gstep.gekin < 0.001) newParticle = kTRUE;
152 if (TMath::Abs(gstep.vect[2]) > 30) newParticle = kTRUE;
153 }
154
155 //save the Tree header. The file will be automatically closed
156 //when going out of the function scope
157 t2.Write();
158}
159
160void tree2r()
161{
162 //read the Tree generated by tree2w and fill one histogram
163 //we are only interested by the destep branch.
164
165 //note that we use "new" to create the TFile and TTree objects !
166 //because we want to keep these objects alive when we leave
167 //this function.
168 TFile *f = new TFile("tree2.root");
169 TTree *t2 = (TTree*)f->Get("t2");
170 static Float_t destep;
171 TBranch *b_destep = t2->GetBranch("destep");
172 b_destep->SetAddress(&destep);
173
174 //create one histogram
175 TH1F *hdestep = new TH1F("hdestep","destep in Mev",100,1e-5,3e-5);
176
177 //read only the destep branch for all entries
179 for (Long64_t i=0;i<nentries;i++) {
180 b_destep->GetEntry(i);
181 hdestep->Fill(destep);
182 }
183
184 //we do not close the file.
185 //We want to keep the generated histograms
186 //We fill a 3-d scatter plot with the particle step coordinates
187 TCanvas *c1 = new TCanvas("c1","c1",600,800);
188 c1->SetFillColor(42);
189 c1->Divide(1,2);
190 c1->cd(1);
191 hdestep->SetFillColor(45);
192 hdestep->Fit("gaus");
193 c1->cd(2);
194 gPad->SetFillColor(37);
195 t2->SetMarkerColor(kRed);
196 t2->Draw("vect[0]:vect[1]:vect[2]");
197
198 // Allow to use the TTree after the end of the function.
200}
201
202void tree2() {
203 tree2w();
204 tree2r();
205}
#define f(i)
Definition: RSha256.hxx:104
#define e(i)
Definition: RSha256.hxx:103
bool Bool_t
Definition: RtypesCore.h:63
int Int_t
Definition: RtypesCore.h:45
const Bool_t kFALSE
Definition: RtypesCore.h:101
float Float_t
Definition: RtypesCore.h:57
long long Long64_t
Definition: RtypesCore.h:80
const Bool_t kTRUE
Definition: RtypesCore.h:100
@ kRed
Definition: Rtypes.h:66
winID h TVirtualViewer3D TVirtualGLPainter p
int nentries
Definition: THbookFile.cxx:91
R__EXTERN TRandom * gRandom
Definition: TRandom.h:62
#define gPad
Definition: TVirtualPad.h:288
virtual void SetFillColor(Color_t fcolor)
Set the fill area color.
Definition: TAttFill.h:37
virtual void SetMarkerColor(Color_t mcolor=1)
Set the marker color.
Definition: TAttMarker.h:38
A TTree is a list of TBranches.
Definition: TBranch.h:89
virtual Int_t GetEntry(Long64_t entry=0, Int_t getall=0)
Read all leaves of entry and return total number of bytes read.
Definition: TBranch.cxx:1644
virtual void SetAddress(void *add)
Set address of this branch.
Definition: TBranch.cxx:2599
The Canvas class.
Definition: TCanvas.h:23
A ROOT file is a suite of consecutive data records (TKey instances) with a well defined format.
Definition: TFile.h:54
1-D histogram with a float per channel (see TH1 documentation)}
Definition: TH1.h:574
virtual TFitResultPtr Fit(const char *formula, Option_t *option="", Option_t *goption="", Double_t xmin=0, Double_t xmax=0)
Fit histogram with function fname.
Definition: TH1.cxx:3894
virtual Int_t Fill(Double_t x)
Increment bin with abscissa X by 1.
Definition: TH1.cxx:3338
virtual Double_t Gaus(Double_t mean=0, Double_t sigma=1)
Samples a random number from the standard Normal (Gaussian) Distribution with the given mean and sigm...
Definition: TRandom.cxx:274
Double_t Rndm() override
Machine independent random number generator.
Definition: TRandom.cxx:552
A TTree represents a columnar dataset.
Definition: TTree.h:79
virtual TBranch * GetBranch(const char *name)
Return pointer to the branch with the given name in this tree or its friends.
Definition: TTree.cxx:5262
void Draw(Option_t *opt) override
Default Draw method for all objects.
Definition: TTree.h:428
virtual Long64_t GetEntries() const
Definition: TTree.h:459
virtual void ResetBranchAddresses()
Tell all of our branches to drop their current objects and allocate new ones.
Definition: TTree.cxx:8049
return c1
Definition: legend1.C:41
TF1 * f1
Definition: legend1.C:11
Double_t Sqrt(Double_t x)
Returns the square root of x.
Definition: TMath.h:660
Short_t Abs(Short_t d)
Returns the absolute value of parameter Short_t d.
Definition: TMathBase.h:123
TLine l
Definition: textangle.C:4
#define snext(osub1, osub2)
Definition: triangle.c:1168