Detailed Description

Example showing how to write and read a std vector of ROOT::Math LorentzVector in a ROOT tree.

In the write() function a variable number of track Vectors is generated according to a Poisson distribution with random momentum uniformly distributed in phi and eta. In the read() the vectors are read back and the content analysed and some information such as number of tracks per event or the track pt distributions are displayed in a canvas.

To execute the macro type in:

root[0]: .x mathcoreVectorCollection.C

Processing /mnt/build/workspace/root-makedoc-v614/rootspi/rdoc/src/v6-14-00-patches/tutorials/math/mathcoreVectorCollection.C...
 Time for new Vector 0.128322  0.13
******************************************************************************
*Tree    :t1        : Tree with new LorentzVector                            *
*Entries :    10000 : Total =         1854288 bytes  File  Size =    1837797 *
*        :          : Tree compression factor =   1.01                       *
******************************************************************************
*Br    0 :tracks    : Int_t tracks_                                          *
*Entries :    10000 : Total  Size=      84910 bytes  File Size  =      66796 *
*Baskets :        4 : Basket Size=      32000 bytes  Compression=   1.20     *
*............................................................................*
*Br    1 :tracks.fCoordinates.fX : Double_t fX[tracks_]                      *
*Entries :    10000 : Total  Size=     443177 bytes  File Size  =     442360 *
*Baskets :       16 : Basket Size=      32000 bytes  Compression=   1.00     *
*............................................................................*
*Br    2 :tracks.fCoordinates.fY : Double_t fY[tracks_]                      *
*Entries :    10000 : Total  Size=     443177 bytes  File Size  =     442360 *
*Baskets :       16 : Basket Size=      32000 bytes  Compression=   1.00     *
*............................................................................*
*Br    3 :tracks.fCoordinates.fZ : Double_t fZ[tracks_]                      *
*Entries :    10000 : Total  Size=     443177 bytes  File Size  =     442360 *
*Baskets :       16 : Basket Size=      32000 bytes  Compression=   1.00     *
*............................................................................*
*Br    4 :tracks.fCoordinates.fT : Double_t fT[tracks_]                      *
*Entries :    10000 : Total  Size=     443177 bytes  File Size  =     442360 *
*Baskets :       16 : Basket Size=      32000 bytes  Compression=   1.00     *
*............................................................................*
 Tree Entries 10000
 Time for new Vector 0.0679669  0.06
(int) 0

#include "TRandom.h"
#include "TStopwatch.h"
#include "TSystem.h"
#include "TFile.h"
#include "TTree.h"
#include "TH1D.h"
#include "TCanvas.h"
#include "TMath.h"
#include <iostream>
// CINT does not understand some files included by LorentzVector
#include "Math/Vector3D.h"
#include "Math/Vector4D.h"
using namespace ROOT::Math;
double write(int n) {
   TRandom R;
   TStopwatch timer;
   TFile f1("mathcoreLV.root","RECREATE");
   // create tree
   TTree t1("t1","Tree with new LorentzVector");
   std::vector<ROOT::Math::XYZTVector>  tracks;
   std::vector<ROOT::Math::XYZTVector> * pTracks = &tracks;
   t1.Branch("tracks","std::vector<ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > >",&pTracks);
   double M = 0.13957;  // set pi+ mass
   timer.Start();
   double sum = 0;
   for (int i = 0; i < n; ++i) {
      int nPart = R.Poisson(5);
      pTracks->clear();
      pTracks->reserve(nPart);
      for (int j = 0; j < nPart; ++j) {
         double px = R.Gaus(0,10);
         double py = R.Gaus(0,10);
         double pt = sqrt(px*px +py*py);
         double eta = R.Uniform(-3,3);
         double phi = R.Uniform(0.0 , 2*TMath::Pi() );
         RhoEtaPhiVector vcyl( pt, eta, phi);
         // set energy
         double E = sqrt( vcyl.R()*vcyl.R() + M*M);
         XYZTVector q( vcyl.X(), vcyl.Y(), vcyl.Z(), E);
         // fill track vector
         pTracks->push_back(q);
         // evaluate sum of components to check
         sum += q.x()+q.y()+q.z()+q.t();
      }
      t1.Fill();
   }
   f1.Write();
   timer.Stop();
   std::cout << " Time for new Vector " << timer.RealTime() << "  " << timer.CpuTime() << std::endl;
   t1.Print();
   return sum;
}
double read() {
   TRandom R;
   TStopwatch timer;
   TH1D * h1 = new TH1D("h1","total event  energy ",100,0,1000.);
   TH1D * h2 = new TH1D("h2","Number of track per event",21,-0.5,20.5);
   TH1D * h3 = new TH1D("h3","Track Energy",100,0,200);
   TH1D * h4 = new TH1D("h4","Track Pt",100,0,100);
   TH1D * h5 = new TH1D("h5","Track Eta",100,-5,5);
   TH1D * h6 = new TH1D("h6","Track Cos(theta)",100,-1,1);
   TFile f1("mathcoreLV.root");
   // create tree
   TTree *t1 = (TTree*)f1.Get("t1");
   std::vector<ROOT::Math::LorentzVector<ROOT::Math::PxPyPzE4D<double> > > * pTracks = 0;
   t1->SetBranchAddress("tracks",&pTracks);
   timer.Start();
   int n = (int) t1->GetEntries();
   std::cout << " Tree Entries " << n << std::endl;
   double sum=0;
   for (int i = 0; i < n; ++i) {
      t1->GetEntry(i);
      int ntrk = pTracks->size();
      h3->Fill(ntrk);
      XYZTVector q;
      for (int j = 0; j < ntrk; ++j) {
         XYZTVector v = (*pTracks)[j];
         q += v;
         h3->Fill(v.E());
         h4->Fill(v.Pt());
         h5->Fill(v.Eta());
         h6->Fill(cos(v.Theta()));
         sum += v.x() + v.y() + v.z() + v.t();
      }
      h1->Fill(q.E() );
      h2->Fill(ntrk);
   }
   timer.Stop();
   std::cout << " Time for new Vector " << timer.RealTime() << "  " << timer.CpuTime() << std::endl;
   TCanvas *c1 = new TCanvas("c1","demo of Trees",10,10,600,800);
   c1->Divide(2,3);
   c1->cd(1);
   h1->Draw();
   c1->cd(2);
   h2->Draw();
   c1->cd(3);
   h3->Draw();
   c1->cd(3);
   h3->Draw();
   c1->cd(4);
   h4->Draw();
   c1->cd(5);
   h5->Draw();
   c1->cd(6);
   h6->Draw();
   return sum;
}
int mathcoreVectorCollection() {
   int nEvents = 10000;
   double s1 = write(nEvents);
   double s2 = read();
   if (fabs(s1-s2) > s1*1.E-15 ) {
      std::cout << "ERROR: Found difference in Vector when reading  ( " << s1 << " != " << s2 << " diff = " << fabs(s1-s2) << " ) " << std::endl;
      return -1;
   }
   return 0;
}
int main() {
   return mathcoreVectorCollection();
}

Author: Andras Zsenei

Definition in file mathcoreVectorCollection.C.