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Reference Guide
tree2a.C
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1/// \file
2/// \ingroup tutorial_tree
3/// \notebook
4/// This example is the same as tree2.C, but uses a class instead of a C-struct.
5/// In this example, we are mapping a class to one of the Geant3
6/// common blocks /gctrak/. In the real life, this common will be filled
7/// by Geant3 at each step and only the Tree Fill function should be called.
8/// The example emulates the Geant3 step routines.
9///
10/// to run the example, do to execute with native compiler:
11/// ~~~
12/// .x tree2a.C+
13/// ~~~
14///
15/// Note that since IO is involved, ACLiC has to be invoked to create the dictionary of class Gctrak.
16/// \macro_code
17///
18/// \author Rene Brun
19
20#include "TROOT.h"
21#include "TFile.h"
22#include "TTree.h"
23#include "TBrowser.h"
24#include "TH2.h"
25#include "TMath.h"
26#include "TRandom.h"
27#include "TCanvas.h"
28
29const Int_t MAXMEC = 30;
30
31class Gctrak : public TObject {
32public:
33 Float_t vect[7];
34 Float_t getot;
35 Float_t gekin;
36 Float_t vout[7]; //! not persistent
37 Int_t nmec;
38 Int_t *lmec; //[nmec]
39 Int_t *namec; //[nmec]
40 Int_t nstep; //! not persistent
41 Int_t pid;
42 Float_t destep;
43 Float_t destel; //! not persistent
44 Float_t safety; //! not persistent
45 Float_t sleng; //! not persistent
46 Float_t step; //! not persistent
47 Float_t snext; //! not persistent
48 Float_t sfield; //! not persistent
49 Float_t tofg; //! not persistent
50 Float_t gekrat; //! not persistent
51 Float_t upwght; //! not persistent
52
53 Gctrak() {lmec=0; namec=0;}
54
55 ClassDef(Gctrak,1)
56};
57
58
59void helixStep(Float_t step, Float_t *vect, Float_t *vout)
60{
61 // extrapolate track in constant field
62 Float_t field = 20; //magnetic field in kilogauss
63 enum Evect {kX,kY,kZ,kPX,kPY,kPZ,kPP};
64 vout[kPP] = vect[kPP];
65 Float_t h4 = field*2.99792e-4;
66 Float_t rho = -h4/vect[kPP];
67 Float_t tet = rho*step;
68 Float_t tsint = tet*tet/6;
69 Float_t sintt = 1 - tsint;
70 Float_t sint = tet*sintt;
71 Float_t cos1t = tet/2;
72 Float_t f1 = step*sintt;
73 Float_t f2 = step*cos1t;
74 Float_t f3 = step*tsint*vect[kPZ];
75 Float_t f4 = -tet*cos1t;
76 Float_t f5 = sint;
77 Float_t f6 = tet*cos1t*vect[kPZ];
78 vout[kX] = vect[kX] + (f1*vect[kPX] - f2*vect[kPY]);
79 vout[kY] = vect[kY] + (f1*vect[kPY] + f2*vect[kPX]);
80 vout[kZ] = vect[kZ] + (f1*vect[kPZ] + f3);
81 vout[kPX] = vect[kPX] + (f4*vect[kPX] - f5*vect[kPY]);
82 vout[kPY] = vect[kPY] + (f4*vect[kPY] + f5*vect[kPX]);
83 vout[kPZ] = vect[kPZ] + (f4*vect[kPZ] + f6);
84}
85
86void tree2aw()
87{
88 //create a Tree file tree2.root
89
90 //create the file, the Tree and a few branches with
91 //a subset of gctrak
92 TFile f("tree2.root","recreate");
93 TTree t2("t2","a Tree with data from a fake Geant3");
94 Gctrak *gstep = new Gctrak;
95 t2.Branch("track",&gstep,8000,1);
96
97 //Initialize particle parameters at first point
98 Float_t px,py,pz,p,charge=0;
99 Float_t vout[7];
100 Float_t mass = 0.137;
101 Bool_t newParticle = kTRUE;
102 gstep->lmec = new Int_t[MAXMEC];
103 gstep->namec = new Int_t[MAXMEC];
104 gstep->step = 0.1;
105 gstep->destep = 0;
106 gstep->nmec = 0;
107 gstep->pid = 0;
108
109 //transport particles
110 for (Int_t i=0;i<10000;i++) {
111 //generate a new particle if necessary
112 if (newParticle) {
113 px = gRandom->Gaus(0,.02);
114 py = gRandom->Gaus(0,.02);
115 pz = gRandom->Gaus(0,.02);
116 p = TMath::Sqrt(px*px+py*py+pz*pz);
117 charge = 1; if (gRandom->Rndm() < 0.5) charge = -1;
118 gstep->pid += 1;
119 gstep->vect[0] = 0;
120 gstep->vect[1] = 0;
121 gstep->vect[2] = 0;
122 gstep->vect[3] = px/p;
123 gstep->vect[4] = py/p;
124 gstep->vect[5] = pz/p;
125 gstep->vect[6] = p*charge;
126 gstep->getot = TMath::Sqrt(p*p + mass*mass);
127 gstep->gekin = gstep->getot - mass;
128 newParticle = kFALSE;
129 }
130
131 // fill the Tree with current step parameters
132 t2.Fill();
133
134 //transport particle in magnetic field
135 helixStep(gstep->step, gstep->vect, vout); //make one step
136
137 //apply energy loss
138 gstep->destep = gstep->step*gRandom->Gaus(0.0002,0.00001);
139 gstep->gekin -= gstep->destep;
140 gstep->getot = gstep->gekin + mass;
141 gstep->vect[6] = charge*TMath::Sqrt(gstep->getot*gstep->getot - mass*mass);
142 gstep->vect[0] = vout[0];
143 gstep->vect[1] = vout[1];
144 gstep->vect[2] = vout[2];
145 gstep->vect[3] = vout[3];
146 gstep->vect[4] = vout[4];
147 gstep->vect[5] = vout[5];
148 gstep->nmec = (Int_t)(5*gRandom->Rndm());
149 for (Int_t l=0;l<gstep->nmec;l++) {
150 gstep->lmec[l] = l;
151 gstep->namec[l] = l+100;
152 }
153 if (gstep->gekin < 0.001) newParticle = kTRUE;
154 if (TMath::Abs(gstep->vect[2]) > 30) newParticle = kTRUE;
155 }
156
157 //save the Tree header. The file will be automatically closed
158 //when going out of the function scope
159 t2.Write();
160}
161
162void tree2ar()
163{
164 //read the Tree generated by tree2w and fill one histogram
165 //we are only interested by the destep branch.
166
167 //note that we use "new" to create the TFile and TTree objects !
168 //because we want to keep these objects alive when we leave
169 //this function.
170 TFile *f = new TFile("tree2.root");
171 TTree *t2 = (TTree*)f->Get("t2");
172 Gctrak *gstep = 0;
173 t2->SetBranchAddress("track",&gstep);
174 TBranch *b_destep = t2->GetBranch("destep");
175
176 //create one histogram
177 TH1F *hdestep = new TH1F("hdestep","destep in Mev",100,1e-5,3e-5);
178
179 //read only the destep branch for all entries
181 for (Long64_t i=0;i<nentries;i++) {
182 b_destep->GetEntry(i);
183 hdestep->Fill(gstep->destep);
184 }
185
186 //we do not close the file.
187 //We want to keep the generated histograms
188 //We fill a 3-d scatter plot with the particle step coordinates
189 TCanvas *c1 = new TCanvas("c1","c1",600,800);
190 c1->SetFillColor(42);
191 c1->Divide(1,2);
192 c1->cd(1);
193 hdestep->SetFillColor(45);
194 hdestep->Fit("gaus");
195 c1->cd(2);
196 gPad->SetFillColor(37);
197 t2->SetMarkerColor(kRed);
198 t2->Draw("vect[0]:vect[1]:vect[2]");
199 if (gROOT->IsBatch()) return;
200
201 // invoke the x3d viewer
202 gPad->GetViewer3D("x3d");
203}
204
205void tree2a() {
206 tree2aw();
207 tree2ar();
208}
#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
#define ClassDef(name, id)
Definition: Rtypes.h:335
@ kRed
Definition: Rtypes.h:66
winID h TVirtualViewer3D TVirtualGLPainter p
int nentries
Definition: THbookFile.cxx:91
#define gROOT
Definition: TROOT.h:404
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
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
Mother of all ROOT objects.
Definition: TObject.h:37
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 Int_t SetBranchAddress(const char *bname, void *add, TBranch **ptr=0)
Change branch address, dealing with clone trees properly.
Definition: TTree.cxx:8354
virtual Long64_t GetEntries() const
Definition: TTree.h:459
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