JetClustering.cc

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#include <vector>
#include <string>

#include <fastjet/JetDefinition.hh>
#include <fastjet/PseudoJet.hh>
#include <fastjet/ClusterSequence.hh>
#include <fastjet/SISConePlugin.hh>

#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/Utilities/interface/Exception.h"

#include "GeneratorInterface/LHEInterface/interface/JetInput.h"
#include "GeneratorInterface/LHEInterface/interface/JetClustering.h"

namespace lhef {

class JetClustering::Algorithm {
    public:
    typedef JetClustering::Jet      Jet;
    typedef JetClustering::ParticleVector   ParticleVector;

    Algorithm(const edm::ParameterSet &params, double jetPtMin) :
        jetPtMin(jetPtMin) {}
    virtual ~Algorithm() {}

    virtual std::vector<Jet> operator () (
                const ParticleVector &input) const = 0;

    double getJetPtMin() const { return jetPtMin; }

    private:
    double  jetPtMin;
};

namespace {
    class FastJetAlgorithmWrapper : public JetClustering::Algorithm {
        public:
        FastJetAlgorithmWrapper(const edm::ParameterSet &params,
                                double jetPtMin);
        ~FastJetAlgorithmWrapper() {}

        protected:
        std::vector<Jet> operator () (
                const ParticleVector &input) const;

        std::auto_ptr<fastjet::JetDefinition::Plugin>   plugin;
        std::auto_ptr<fastjet::JetDefinition>       jetDefinition;
    };

    class KtAlgorithm : public FastJetAlgorithmWrapper {
        public:
        KtAlgorithm(const edm::ParameterSet &params,
                    double jetPtMin);
        ~KtAlgorithm() {}
    };

    class SISConeAlgorithm : public FastJetAlgorithmWrapper {
        public:
        SISConeAlgorithm(const edm::ParameterSet &params,
                         double jetPtMin);
        ~SISConeAlgorithm() {}

        private:
        static fastjet::SISConePlugin::SplitMergeScale
                    getScale(const std::string &name);
    };
} // anonymous namespace

FastJetAlgorithmWrapper::FastJetAlgorithmWrapper(
            const edm::ParameterSet &params, double jetPtMin) :
    JetClustering::Algorithm(params, jetPtMin)
{
}

std::vector<JetClustering::Jet> FastJetAlgorithmWrapper::operator () (
                    const ParticleVector &input) const
{
    if (input.empty())
        return std::vector<JetClustering::Jet>();

    std::vector<fastjet::PseudoJet> jfInput;
    jfInput.reserve(input.size());
    for(ParticleVector::const_iterator iter = input.begin();
        iter != input.end(); ++iter) {
        jfInput.push_back(fastjet::PseudoJet(
            (*iter)->momentum().px(), (*iter)->momentum().py(),
            (*iter)->momentum().pz(), (*iter)->momentum().e()));
        jfInput.back().set_user_index(iter - input.begin());
    }

    fastjet::ClusterSequence sequence(jfInput, *jetDefinition);
    std::vector<fastjet::PseudoJet> jets =
                sequence.inclusive_jets(getJetPtMin());

    std::vector<Jet> result;
    result.reserve(jets.size());
    ParticleVector constituents;
    for(std::vector<fastjet::PseudoJet>::const_iterator iter = jets.begin();
        iter != jets.end(); ++iter) {
        std::vector<fastjet::PseudoJet> fjConstituents =
                    sequence.constituents(*iter);
        unsigned int size = fjConstituents.size();
        constituents.resize(size);
        for(unsigned int i = 0; i < size; i++)
            constituents[i] =
                input[fjConstituents[i].user_index()];

        result.push_back(
            Jet(iter->px(), iter->py(), iter->pz(), iter->E(),
                constituents));
    }

    return result;
}

KtAlgorithm::KtAlgorithm(const edm::ParameterSet &params, double jetPtMin) :
    FastJetAlgorithmWrapper(params, jetPtMin)
{
    jetDefinition.reset(new fastjet::JetDefinition(
                fastjet::kt_algorithm,
                params.getParameter<double>("ktRParam"),
                fastjet::Best));
}

SISConeAlgorithm::SISConeAlgorithm(
            const edm::ParameterSet &params, double jetPtMin) :
    FastJetAlgorithmWrapper(params, jetPtMin)
{
    std::string splitMergeScale = 
            params.getParameter<std::string>("splitMergeScale");
    fastjet::SISConePlugin::SplitMergeScale scale;

    if (splitMergeScale == "pt")
        scale = fastjet::SISConePlugin::SM_pt;
    else if (splitMergeScale == "Et")
        scale = fastjet::SISConePlugin::SM_Et;
    else if (splitMergeScale == "mt")
        scale = fastjet::SISConePlugin::SM_mt;
    else if (splitMergeScale == "pttilde")
        scale = fastjet::SISConePlugin::SM_pttilde;
    else
        throw cms::Exception("Configuration") 
            << "JetClustering SISCone scale '" << splitMergeScale
            << "' unknown." << std::endl;

    plugin.reset(new fastjet::SISConePlugin(
            params.getParameter<double>("coneRadius"), 
            params.getParameter<double>("coneOverlapThreshold"),
            params.getParameter<int>("maxPasses"),
            params.getParameter<double>("protojetPtMin"),
            params.getParameter<bool>("caching"),
            scale));
    jetDefinition.reset(new fastjet::JetDefinition(plugin.get()));
}

JetClustering::JetClustering(const edm::ParameterSet &params)
{
    double jetPtMin = params.getParameter<double>("jetPtMin");
    init(params, jetPtMin);
}

JetClustering::JetClustering(const edm::ParameterSet &params,
                             double jetPtMin)
{
    init(params, jetPtMin);
}

JetClustering::~JetClustering()
{
}

void JetClustering::init(const edm::ParameterSet &params, double jetPtMin)
{
    edm::ParameterSet algoParams =
            params.getParameter<edm::ParameterSet>("algorithm");
    std::string algoName = algoParams.getParameter<std::string>("name");

    if (algoName == "KT")
        jetAlgo.reset(new KtAlgorithm(algoParams, jetPtMin));
    else if (algoName == "SISCone")
        jetAlgo.reset(new SISConeAlgorithm(algoParams, jetPtMin));
    else
        throw cms::Exception("Configuration")
            << "JetClustering algorithm \"" << algoName
            << "\" unknown." << std::endl;
}

double JetClustering::getJetPtMin() const
{
    return jetAlgo->getJetPtMin();
}

std::vector<JetClustering::Jet> JetClustering::operator () (
                    const ParticleVector &input) const
{
    return (*jetAlgo)(input);
}

} // namespace lhef