Library Interface

Here is an explanation of how Delphes' library can be called from a program.

Installation

Commands to download and build the library:

setup ROOT environment variables

wget --no-check-certificate https://cp3.irmp.ucl.ac.be/projects/delphes/raw-attachment/wiki/WikiStart/Delphes-3.0.0.tar.gz
tar -zxf Delphes-3.0.0.tar.gz

cd Delphes-3.0.0
make -j 4

# library
ls libDelphes.so

# headers
ls modules/Delphes.h
ls classes/DelphesClasses.h
ls classes/DelphesFactory.h

# config file
ls examples/delphes_card_CMS.tcl

Complete example

A fully functional application using the Delphes library can be found in

readers/DelphesSTDHEP.cpp

Simplified example

ReadEvent, ReadParticle, ConvertInput and ConvertOutput functions should be implemented by the library's user.

#include <stdexcept>
#include <iostream>

#include "TROOT.h"
#include "TApplication.h"

#include "TObjArray.h"
#include "TDatabasePDG.h"
#include "TParticlePDG.h"
#include "TLorentzVector.h"

#include "modules/Delphes.h"
#include "classes/DelphesClasses.h"
#include "classes/DelphesFactory.h"

using namespace std;

void ConvertInput(DelphesFactory *factory, TObjArray *particleOutputArray, TObjArray *candidateOutputArray, TObjArray *partonOutputArray);

void ConvertOutput(Delphes *modularDelphes);

bool ReadEvent() { return true; }

bool ReadParticle() { return true; }

int main()
{
  // Declaration of variables
  ExRootConfReader *confReader;
  Delphes *modularDelphes;
  DelphesFactory *factory;
  TObjArray *particleOutputArray;
  TObjArray *candidateOutputArray;
  TObjArray *partonOutputArray;

  gROOT->SetBatch();

  int appargc = 1;
  char *appName = "DelphesExample";
  char *appargv[] = {appName};
  TApplication app(appName, &appargc, appargv);

  try
  {
    // Initialization
    confReader = new ExRootConfReader;
    confReader->ReadFile("examples/delphes_card_CMS.tcl");

    modularDelphes = new Delphes("Delphes");
    modularDelphes->SetConfReader(confReader);
    
    factory = modularDelphes->GetFactory();

    particleOutputArray = modularDelphes->ExportArray("particles");
    candidateOutputArray = modularDelphes->ExportArray("candidates");
    partonOutputArray = modularDelphes->ExportArray("partons");

    modularDelphes->InitTask();

    // Event loop
    while(ReadEvent())
    {
      modularDelphes->Clear();
      ConvertInput(factory, particleOutputArray, candidateOutputArray, partonOutputArray); 
      modularDelphes->ProcessTask();
      ConvertOutput(modularDelphes);
    }

    // Finalization
    modularDelphes->FinishTask();
    delete modularDelphes;
    delete confReader;
    return 0;
  }
  catch(runtime_error &e)
  {
    cerr << "** ERROR: " << e.what() << endl;
    return 1;
  }
}

void ConvertInput(DelphesFactory *factory, TObjArray *particleOutputArray, TObjArray *candidateOutputArray, TObjArray *partonOutputArray)
{
  Candidate *candidate;
  TDatabasePDG *pdg;
  TParticlePDG *pdgParticle;
  Int_t pid, status;
  Double_t px, py, pz, e;
  Double_t x, y, z, t;  

  pdg = TDatabasePDG::Instance()
  
  while(ReadParticle())
  {
    if(status == 1 || status == 2)
    {
      candidate = factory->NewCandidate();

      candidate->PID = pid;

      candidate->Status = status;

      
      pdgParticle = pdg->GetParticle(fPID);
      candidate->Charge = pdgParticle ? Int_t(pdgParticle->Charge()/3.0) : -999;
      candidate->Mass = pdgParticle ? pdgParticle->Mass() : -999.9;
  
      candidate->Momentum.SetPxPyPzE(px, py, pz, e);

      candidate->Position.SetXYZT(x, y, z, t);

      particleOutputArray->Add(candidate);

      if(!pdgParticle) return;

      if(status == 1)
      {
        candidateOutputArray->Add(candidate);
      }
      else if(status == 2)
      {
        partonOutputArray->Add(candidate);
      }
    }
  }
}

void ConvertOutput(Delphes *modularDelphes)
{
  const TObjArray *arrayJets = modularDelphes->ImportArray("FastJetFinder/jets");
  TIter iteratorJets(arrayJets);
  Candidate *candidate;

  iteratorJets.Reset();
  while((candidate = static_cast<Candidate*>(iteratorJets.Next())))
  {
    const TLorentzVector &momentum = candidate->GetMomentum();
  }
}