mathcoreVectorCollection.C

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/// \file
/// \ingroup tutorial_math
/// \notebook -js
/// 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:
///
/// ~~~{.cpp}
///   root[0]: .x  mathcoreVectorCollection.C
/// ~~~
///
/// \macro_image
/// \macro_output
/// \macro_code
///
/// \author Andras Zsenei
 
#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>
 
// CLING 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 * 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 = nullptr;
   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();
      XYZTVector q;
      for (int j = 0; j < ntrk; ++j) {
         XYZTVector v = (*pTracks)[j];
         q += v;
         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() );
   }
 
   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);
   c1->cd(3);
   c1->cd(3);
   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();
}