Library Interface

Introduction

Delphes can be used as a library and be included in a third party application. To do so, simply download and compile Delphes as explained in the Quick Tour.

This creates among other things the libDelphes.so library that can be dynamically linked to any C++ binary. Header files are located in the modules and classes subdirectories:

• modules/Delphes.h
• classes/DelphesClasses.h
• classes/DelphesFactory.h

Simplified example

The code below shows the basic ingredients to build a standalone application using Delphes. In that template, the ReadEvent, ReadParticle, ConvertInput and ConvertOutput functions should be implemented by the 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 *allParticleOutputArray,
  TObjArray *stableParticleOutputArray, 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 *allParticleOutputArray;
  TObjArray *stableParticleOutputArray;
  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("cards/delphes_card_CMS.tcl");

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

    factory = modularDelphes->GetFactory();

    allParticleOutputArray = modularDelphes->ExportArray("allParticles");
    stableParticleOutputArray = modularDelphes->ExportArray("stableParticles");
    partonOutputArray = modularDelphes->ExportArray("partons");

    modularDelphes->InitTask();

    // Event loop
    while(ReadEvent())
    {
      modularDelphes->Clear();
      ConvertInput(factory, allParticleOutputArray,
        stableParticleOutputArray, 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 *allParticleOutputArray,
  TObjArray *stableParticleOutputArray, TObjArray *partonOutputArray)
{
  Candidate *candidate;
  TDatabasePDG *pdg;
  TParticlePDG *pdgParticle;
  Int_t pdgCode;

  Int_t pid, status;
  Double_t px, py, pz, e, mass;
  Double_t x, y, z, t;

  pdg = TDatabasePDG::Instance();

  while(ReadParticle())
  {
    candidate = factory->NewCandidate();

    candidate->PID = pid;
    pdgCode = TMath::Abs(candidate->PID);

    candidate->Status = status;

    pdgParticle = pdg->GetParticle(pid);
    candidate->Charge = pdgParticle ? Int_t(pdgParticle->Charge()/3.0) : -999;
    candidate->Mass = mass;

    candidate->Momentum.SetPxPyPzE(px, py, pz, e);

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

    allParticleOutputArray->Add(candidate);

    if(!pdgParticle) return;

    if(status == 1)
    {
      stableParticleOutputArray->Add(candidate);
    }
    else if(pdgCode <= 5 || pdgCode == 21 || pdgCode == 15)
    {
      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->Momentum;
  }
}

Complete example

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

readers/DelphesSTDHEP.cpp