MatcherUsingTracksAlgorithm.cc

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#include "MuonAnalysis/MuonAssociators/interface/MatcherUsingTracksAlgorithm.h"

#include "DataFormats/Math/interface/deltaR.h"
#include "DataFormats/Math/interface/deltaPhi.h"

#include "DataFormats/RecoCandidate/interface/RecoCandidate.h"
#include "DataFormats/TrackReco/interface/Track.h"

#include "TrackingTools/Records/interface/TrackingComponentsRecord.h"
#include "MagneticField/Records/interface/IdealMagneticFieldRecord.h"
#include "Geometry/Records/interface/GlobalTrackingGeometryRecord.h"
#include "TrackingTools/TrajectoryState/interface/TrajectoryStateTransform.h"
#include "TrackingTools/PatternTools/interface/TSCPBuilderNoMaterial.h"
#include "TrackingTools/TrajectoryState/interface/PerigeeConversions.h"

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


MatcherUsingTracksAlgorithm::MatcherUsingTracksAlgorithm(const edm::ParameterSet & iConfig) :
    whichTrack1_(None),     whichTrack2_(None), 
    whichState1_(AtVertex), whichState2_(AtVertex),
    srcCut_(iConfig.existsAs<std::string>("srcPreselection") ? iConfig.getParameter<std::string>("srcPreselection") : ""),
    matchedCut_(iConfig.existsAs<std::string>("matchedPreselection") ? iConfig.getParameter<std::string>("matchedPreselection") : ""),
    requireSameCharge_(iConfig.existsAs<bool>("requireSameCharge") ? iConfig.getParameter<bool>("requireSameCharge") : false)
{
    std::string algo = iConfig.getParameter<std::string>("algorithm");
    if      (algo == "byTrackRef")           { algo_ = ByTrackRef; }
    else if (algo == "byPropagatingSrc")     { algo_ = ByPropagatingSrc; }
    else if (algo == "byPropagatingMatched") { algo_ = ByPropagatingMatched; }
    else if (algo == "byDirectComparison")   { algo_ = ByDirectComparison; }
    else throw cms::Exception("Configuration") << "Value '" << algo << "' for algorithm not yet implemented.\n";

    getConf(iConfig, "src",     whichTrack1_, whichState1_);
    getConf(iConfig, "matched", whichTrack2_, whichState2_);

    if (algo_ == ByTrackRef) {
        // validate the config
        if (whichTrack1_ == None || whichTrack2_ == None) throw cms::Exception("Configuration") << "Algorithm 'byTrackRef' needs tracks not to be 'none'.\n";
    } else if (algo_ == ByPropagatingSrc || algo_ == ByPropagatingMatched || algo_ == ByDirectComparison) {
        // read matching cuts
        maxLocalPosDiff_      = iConfig.getParameter<double>("maxDeltaLocalPos");
        maxGlobalMomDeltaR_   = iConfig.getParameter<double>("maxDeltaR");
        maxGlobalMomDeltaEta_ = iConfig.existsAs<double>("maxDeltaEta") ? iConfig.getParameter<double>("maxDeltaEta") : maxGlobalMomDeltaR_;
        maxGlobalMomDeltaPhi_ = iConfig.existsAs<double>("maxDeltaPhi") ? iConfig.getParameter<double>("maxDeltaPhi") : maxGlobalMomDeltaR_;
        maxGlobalDPtRel_      = iConfig.getParameter<double>("maxDeltaPtRel");

        // choice of sorting variable
        std::string sortBy = iConfig.getParameter<std::string>("sortBy");
        if      (sortBy == "deltaLocalPos") sortBy_ = LocalPosDiff;
        else if (sortBy == "deltaPtRel")    sortBy_ = GlobalDPtRel;
        else if (sortBy == "deltaR")        sortBy_ = GlobalMomDeltaR;
        else if (sortBy == "deltaEta")      sortBy_ = GlobalMomDeltaEta;
        else if (sortBy == "deltaPhi")      sortBy_ = GlobalMomDeltaPhi;
        else if (sortBy == "chi2")          sortBy_ = Chi2;
        else throw cms::Exception("Configuration") << "Parameter 'sortBy' must be one of: deltaLocalPos, deltaPtRel, deltaR, chi2.\n";
        // validate the config
        if (algo_ == ByPropagatingSrc) {
            if (whichTrack2_ == None || whichState2_ == AtVertex) {
                algo_ = ByPropagatingSrcTSCP;
                //throw cms::Exception("Configuration") << "Destination track must be non-null, and state must not be 'AtVertex' (not yet).\n";
            }
        } else if (algo_ == ByPropagatingMatched) {
            if (whichTrack1_ == None || whichState1_ == AtVertex) {
                algo_ = ByPropagatingMatchedTSCP;
                //throw cms::Exception("Configuration") << "Destination track must be non-null, and state must not be 'AtVertex' (not yet).\n";
            }
        } else if (algo_ == ByDirectComparison) {
            bool firstAtVertex = (whichTrack1_ == None || whichState1_ == AtVertex);
            bool   secAtVertex = (whichTrack2_ == None || whichState2_ == AtVertex);
            if (firstAtVertex) {
                if (!secAtVertex)  throw cms::Exception("Configuration") << "When using 'byDirectComparison' with 'src' at vertex (or None), 'matched' must be at vertex too.\n";
            } else {
                if (secAtVertex)  throw cms::Exception("Configuration") << "When using 'byDirectComparison' with 'src' not at vertex, 'matched' can't be at vertex or None.\n";
                if (whichState1_ != whichState2_) throw cms::Exception("Configuration") << "You can't use 'byDirectComparison' with non-matching states.\n";
            }
        }

        useChi2_ = iConfig.existsAs<bool>("computeChi2") ? iConfig.getParameter<bool>("computeChi2") : false;
        if (useChi2_) {
           if (whichTrack1_ == None && whichTrack2_ == None) throw cms::Exception("Configuration") << "Can't compute chi2s if both tracks are set to 'none'.\n";
           maxChi2_ = iConfig.getParameter<double>("maxChi2");
           chi2DiagonalOnly_ = iConfig.getParameter<bool>("chi2DiagonalOnly");
           if (algo_ == ByPropagatingSrc || algo_ == ByPropagatingMatched) {
               chi2UseVertex_ = iConfig.getParameter<bool>("chi2UsePosition");
           } else {
               chi2UseVertex_ = iConfig.getParameter<bool>("chi2UseVertex");
               if (algo_ == ByDirectComparison) {
                    std::string choice = iConfig.getParameter<std::string>("chi2MomentumForDxy");
                    if (choice == "src") chi2FirstMomentum_ = true;
                    else if (choice != "matched") throw cms::Exception("Configuration") << "chi2MomentumForDxy must be 'src' or 'matched'\n";
               }
           }
        } else maxChi2_ = 1;

        if (sortBy_ == Chi2 && !useChi2_) throw cms::Exception("Configuration") << "Can't sort by chi2s if 'computeChi2s' is not set to true.\n";
    }
}

void 
MatcherUsingTracksAlgorithm::getConf(const edm::ParameterSet & iConfig, const std::string &whatFor, WhichTrack &whichTrack, WhichState &whichState) {
    std::string s_whichTrack = iConfig.getParameter<std::string>(whatFor+"Track");
    if      (s_whichTrack == "none")    { whichTrack = None; }
    else if (s_whichTrack == "tracker") { whichTrack = TrackerTk; }
    else if (s_whichTrack == "muon")    { whichTrack = MuonTk; }
    else if (s_whichTrack == "global")  { whichTrack = GlobalTk; }
    else throw cms::Exception("Configuration") << "Parameter 'useTrack' must be 'none', 'tracker', 'muon', 'global'\n";
    if ((whichTrack != None) && (algo_ != ByTrackRef)) {
        std::string s_whichState = iConfig.getParameter<std::string>(whatFor+"State");
        if      (s_whichState == "atVertex")  { whichState = AtVertex; }
        else if (s_whichState == "innermost") { whichState = Innermost; }
        else if (s_whichState == "outermost") { whichState = Outermost; }
        else throw cms::Exception("Configuration") << "Parameter 'useState' must be 'atVertex', 'innermost', 'outermost'\n";
    }
}

bool 
MatcherUsingTracksAlgorithm::match(const reco::Candidate &c1, const reco::Candidate &c2, float &deltR, float &deltEta, float &deltPhi, float &deltaLocalPos, float &deltaPtRel, float &chi2) const {
    if (!(srcCut_(c1) && matchedCut_(c2))) return false;
    if (requireSameCharge_ && (c1.charge() != c2.charge())) return false;
    switch (algo_) {
        case ByTrackRef: { 
            reco::TrackRef t1 = getTrack(c1, whichTrack1_); 
            reco::TrackRef t2 = getTrack(c2, whichTrack2_); 
            if (t1.isNonnull()) {
                if (t1 == t2) return true; 
                if (t1.id() != t2.id()) { edm::LogWarning("MatcherUsingTracksAlgorithm") << "Trying to match by reference tracks coming from different collections.\n"; }
            } 
            }
        case ByPropagatingSrc: {
            FreeTrajectoryState start = startingState(c1, whichTrack1_, whichState1_);
            TrajectoryStateOnSurface target = targetState(c2, whichTrack2_, whichState2_);
            return matchWithPropagation(start, target, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2);
            }
        case ByPropagatingMatched: { 
            FreeTrajectoryState start = startingState(c2, whichTrack2_, whichState2_);
            TrajectoryStateOnSurface target = targetState(c1, whichTrack1_, whichState1_);
            return matchWithPropagation(start, target, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2);
            }
        case ByPropagatingSrcTSCP: {
            FreeTrajectoryState start = startingState(c1, whichTrack1_, whichState1_);
            FreeTrajectoryState target = startingState(c2, whichTrack2_, whichState2_);
            return matchWithPropagation(start, target, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2);
            }
        case ByPropagatingMatchedTSCP: { 
            FreeTrajectoryState start = startingState(c2, whichTrack2_, whichState2_);
            FreeTrajectoryState target = startingState(c1, whichTrack1_, whichState1_);
            return matchWithPropagation(start, target, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2);
            }

        case ByDirectComparison: {
            FreeTrajectoryState start = startingState(c1, whichTrack1_, whichState1_);
            FreeTrajectoryState otherstart = startingState(c2, whichTrack2_, whichState2_);
            return matchByDirectComparison(start, otherstart, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2);
            }
    }
    return false;
}

int 
MatcherUsingTracksAlgorithm::match(const reco::Candidate &c1, const edm::View<reco::Candidate> &c2s, float &deltR, float &deltEta, float &deltPhi, float &deltaLocalPos, float &deltaPtRel, float &chi2) const {
    if (!srcCut_(c1)) return -1;
    
    // working and output variables
    FreeTrajectoryState start; TrajectoryStateOnSurface target;
    int match = -1;

    // pre-fetch some states if needed
    if (algo_ == ByPropagatingSrc || algo_ == ByPropagatingSrcTSCP || algo_ == ByPropagatingMatchedTSCP || algo_ == ByDirectComparison) {
        start = startingState(c1, whichTrack1_, whichState1_);
    } else if (algo_ == ByPropagatingMatched) target = targetState(c1, whichTrack1_, whichState1_);

    // loop on the  collection
    edm::View<reco::Candidate>::const_iterator it, ed; int i;
    for (it = c2s.begin(), ed = c2s.end(), i = 0; it != ed; ++it, ++i) {
        if (!matchedCut_(*it)) continue;
        if (requireSameCharge_ && (c1.charge() != it->charge()) ) continue;
        bool exit = false;
        switch (algo_) {
            case ByTrackRef: {
                     reco::TrackRef t1 = getTrack(c1, whichTrack1_); 
                     reco::TrackRef t2 = getTrack(*it, whichTrack2_); 
                     if (t1.isNonnull()) {
                         if (t1 == t2) { match = i; exit = true; }
                         if (t1.id() != t2.id()) { edm::LogWarning("MatcherUsingTracksAlgorithm") << "Trying to match by reference tracks coming from different collections.\n"; }
                     } 
                 } break;
            case ByPropagatingSrc: 
            case ByPropagatingMatched: {
                     if (algo_ == ByPropagatingMatched)  start = startingState(*it, whichTrack2_, whichState2_);
                     else if (algo_ == ByPropagatingSrc) target = targetState(*it, whichTrack2_, whichState2_);
                     if (matchWithPropagation(start, target, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2)) { 
                         match = i; 
                     }
                 } break;
            case ByDirectComparison: {
                     FreeTrajectoryState otherstart = startingState(*it, whichTrack2_, whichState2_);
                     if (matchByDirectComparison(start, otherstart, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2)) {
                         match = i;
                     }
                 } break;
            case ByPropagatingSrcTSCP: {
                    FreeTrajectoryState otherstart = startingState(*it, whichTrack2_, whichState2_);
                    if (matchWithPropagation(start, otherstart, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2)) {
                         match = i;
                    }
                } break;
            case ByPropagatingMatchedTSCP: {
                    FreeTrajectoryState otherstart = startingState(*it, whichTrack2_, whichState2_);
                    if (matchWithPropagation(otherstart, start, deltR, deltEta, deltPhi, deltaLocalPos, deltaPtRel, chi2)) {
                         match = i;
                    }
                } break;
        }
        if (exit) break;
    }

    return match;
}

void 
MatcherUsingTracksAlgorithm::init(const edm::EventSetup & iSetup) {
    iSetup.get<IdealMagneticFieldRecord>().get(magfield_);
    iSetup.get<TrackingComponentsRecord>().get("SteppingHelixPropagatorAny", propagator_);
    iSetup.get<GlobalTrackingGeometryRecord>().get(geometry_);
}


reco::TrackRef
MatcherUsingTracksAlgorithm::getTrack(const reco::Candidate &reco, WhichTrack whichTrack) const {
    reco::TrackRef tk;
    const reco::RecoCandidate *rc = dynamic_cast<const reco::RecoCandidate *>(&reco);
    if (rc == 0) throw cms::Exception("Invalid Data") << "Input object is not a RecoCandidate.\n";
    switch (whichTrack) {
        case TrackerTk: tk = rc->track();          break; 
        case MuonTk   : tk = rc->standAloneMuon(); break;
        case GlobalTk : tk = rc->combinedMuon();   break;
        default: break; // just to make gcc happy
    }
    return tk;
}

FreeTrajectoryState 
MatcherUsingTracksAlgorithm::startingState(const reco::Candidate &reco, WhichTrack whichTrack, WhichState whichState) const {
    FreeTrajectoryState ret;
    if (whichTrack != None) {
        reco::TrackRef tk = getTrack(reco, whichTrack);
        if (tk.isNull()) {
            ret = FreeTrajectoryState();
        } else {
            switch (whichState) {
                case AtVertex:  ret = trajectoryStateTransform::initialFreeState(*tk, magfield_.product()); break;
                case Innermost: ret = trajectoryStateTransform::innerFreeState(  *tk, magfield_.product()); break;
                case Outermost: ret = trajectoryStateTransform::outerFreeState(  *tk, magfield_.product()); break;
            }
        }
    } else {
        ret = FreeTrajectoryState(  GlobalPoint( reco.vx(), reco.vy(), reco.vz()),
                                    GlobalVector(reco.px(), reco.py(), reco.pz()),
                                    reco.charge(),
                                    magfield_.product());
    }
    return ret;
}

TrajectoryStateOnSurface 
MatcherUsingTracksAlgorithm::targetState(const reco::Candidate &reco, WhichTrack whichTrack, WhichState whichState) const {
    TrajectoryStateOnSurface ret;
    reco::TrackRef tk = getTrack(reco, whichTrack);
    if (tk.isNonnull()) {
        switch (whichState) {
            case Innermost: ret = trajectoryStateTransform::innerStateOnSurface(  *tk, *geometry_, magfield_.product()); break;
            case Outermost: ret = trajectoryStateTransform::outerStateOnSurface(  *tk, *geometry_, magfield_.product()); break;
            default: break; // just to make gcc happy
        }
    }
    return ret;
}

bool
MatcherUsingTracksAlgorithm::matchWithPropagation(const FreeTrajectoryState &start, 
                                              const TrajectoryStateOnSurface &target, 
                                              float &lastDeltaR,
                                              float &lastDeltaEta,
                                              float &lastDeltaPhi, 
                                              float &lastDeltaLocalPos,
                                              float &lastGlobalDPtRel,
                                              float &lastChi2) const 
{
    if ((start.momentum().mag() == 0) || !target.isValid()) return false;

    TrajectoryStateOnSurface tsos = propagator_->propagate(start, target.surface());

    bool isBest = false;
    if (tsos.isValid()) {
        float thisLocalPosDiff = (tsos.localPosition()-target.localPosition()).mag();
        float thisGlobalMomDeltaR = deltaR(tsos.globalMomentum(), target.globalMomentum());
        float thisGlobalMomDeltaPhi = fabs(deltaPhi(tsos.globalMomentum().barePhi(), target.globalMomentum().barePhi()));
        float thisGlobalMomDeltaEta = fabs(tsos.globalMomentum().eta() - target.globalMomentum().eta());
        float thisGlobalDPtRel = (tsos.globalMomentum().perp() - target.globalMomentum().perp())/target.globalMomentum().perp();

        if ((thisLocalPosDiff       < maxLocalPosDiff_) &&
            (thisGlobalMomDeltaR    < maxGlobalMomDeltaR_) &&
            (thisGlobalMomDeltaEta  < maxGlobalMomDeltaEta_) &&
            (thisGlobalMomDeltaPhi  < maxGlobalMomDeltaPhi_) &&
            (fabs(thisGlobalDPtRel) < maxGlobalDPtRel_)) {
            float thisChi2         = useChi2_ ? getChi2(target, tsos, chi2DiagonalOnly_, chi2UseVertex_) : 0;
            if (thisChi2 >= maxChi2_) return false;
            switch (sortBy_) {
                case LocalPosDiff:      isBest = (thisLocalPosDiff      < lastDeltaLocalPos); break;
                case GlobalMomDeltaR:   isBest = (thisGlobalMomDeltaR   < lastDeltaR);        break;
                case GlobalMomDeltaEta: isBest = (thisGlobalMomDeltaEta < lastDeltaEta);      break;
                case GlobalMomDeltaPhi: isBest = (thisGlobalMomDeltaPhi < lastDeltaPhi);      break;
                case GlobalDPtRel:      isBest = (thisGlobalDPtRel      < lastGlobalDPtRel);  break;
                case Chi2:              isBest = (thisChi2              < lastChi2);          break;
            }
            if (isBest) {
                lastDeltaLocalPos = thisLocalPosDiff;
                lastDeltaR        = thisGlobalMomDeltaR;
                lastDeltaEta      = thisGlobalMomDeltaEta;
                lastDeltaPhi      = thisGlobalMomDeltaPhi;
                lastGlobalDPtRel  = thisGlobalDPtRel;
                lastChi2          = thisChi2;
            } 
        }  // if match
    }

    return isBest;
}

bool
MatcherUsingTracksAlgorithm::matchWithPropagation(const FreeTrajectoryState &start, 
                                              const FreeTrajectoryState &target, 
                                              float &lastDeltaR,
                                              float &lastDeltaEta,
                                              float &lastDeltaPhi, 
                                              float &lastDeltaLocalPos,
                                              float &lastGlobalDPtRel,
                                              float &lastChi2) const 
{
    if ((start.momentum().mag() == 0) || (target.momentum().mag() == 0)) return false;
    TSCPBuilderNoMaterial propagator;
    /*2.2.X*/ try { 
    TrajectoryStateClosestToPoint tscp = propagator(start, target.position());
    // if (!tscp.isValid()) return false;  // in 3.1.X
    
    bool isBest = false;
    float thisLocalPosDiff = (tscp.position()-target.position()).mag();
    float thisGlobalMomDeltaR   = deltaR(tscp.momentum(), target.momentum());
    float thisGlobalMomDeltaPhi = fabs(deltaPhi(tscp.momentum().barePhi(), target.momentum().barePhi()));
    float thisGlobalMomDeltaEta = fabs(tscp.momentum().eta() - target.momentum().eta());
    float thisGlobalDPtRel = (tscp.momentum().perp() - target.momentum().perp())/target.momentum().perp();

    if ((thisLocalPosDiff       < maxLocalPosDiff_) &&
            (thisGlobalMomDeltaR    < maxGlobalMomDeltaR_) &&
            (thisGlobalMomDeltaEta  < maxGlobalMomDeltaEta_) &&
            (thisGlobalMomDeltaPhi  < maxGlobalMomDeltaPhi_) &&
            (fabs(thisGlobalDPtRel) < maxGlobalDPtRel_)) {
        float thisChi2         = useChi2_ ? getChi2(target, tscp, chi2DiagonalOnly_, chi2UseVertex_) : 0;
        if (thisChi2 >= maxChi2_) return false;
        switch (sortBy_) {
            case LocalPosDiff:      isBest = (thisLocalPosDiff      < lastDeltaLocalPos); break;
            case GlobalMomDeltaR:   isBest = (thisGlobalMomDeltaR   < lastDeltaR);        break;
            case GlobalMomDeltaEta: isBest = (thisGlobalMomDeltaEta < lastDeltaEta);      break;
            case GlobalMomDeltaPhi: isBest = (thisGlobalMomDeltaPhi < lastDeltaPhi);      break;
            case GlobalDPtRel:      isBest = (thisGlobalDPtRel      < lastGlobalDPtRel);  break;
            case Chi2:              isBest = (thisChi2              < lastChi2);          break;
        }
        if (isBest) {
            lastDeltaLocalPos = thisLocalPosDiff;
            lastDeltaR        = thisGlobalMomDeltaR;
            lastDeltaEta      = thisGlobalMomDeltaEta;
            lastDeltaPhi      = thisGlobalMomDeltaPhi;
            lastGlobalDPtRel  = thisGlobalDPtRel;
            lastChi2          = thisChi2;
        } 
    }  // if match

    return isBest;
    /*2.2.X*/ } catch (const TrajectoryStateException &err) { return false; } 
}


bool
MatcherUsingTracksAlgorithm::matchByDirectComparison(const FreeTrajectoryState &start, 
                                                 const FreeTrajectoryState &target, 
                                                 float &lastDeltaR,
                                                 float &lastDeltaEta,
                                                 float &lastDeltaPhi, 
                                                 float &lastDeltaLocalPos,
                                                 float &lastGlobalDPtRel,
                                                 float &lastChi2) const 
{
    if ((start.momentum().mag() == 0) || target.momentum().mag() == 0) return false;

    bool isBest = false;
    float thisLocalPosDiff = (start.position()-target.position()).mag();
    float thisGlobalMomDeltaR   = deltaR(start.momentum(), target.momentum());
    float thisGlobalMomDeltaPhi = fabs(deltaPhi(start.momentum().barePhi(), target.momentum().barePhi()));
    float thisGlobalMomDeltaEta = fabs(start.momentum().eta() - target.momentum().eta());
    float thisGlobalDPtRel = (start.momentum().perp() - target.momentum().perp())/target.momentum().perp();

    if ((thisLocalPosDiff       < maxLocalPosDiff_) &&
            (thisGlobalMomDeltaR    < maxGlobalMomDeltaR_) &&
            (thisGlobalMomDeltaEta  < maxGlobalMomDeltaEta_) &&
            (thisGlobalMomDeltaPhi  < maxGlobalMomDeltaPhi_) &&
            (fabs(thisGlobalDPtRel) < maxGlobalDPtRel_)) {
        float thisChi2 = useChi2_ ? getChi2(start, target, chi2DiagonalOnly_, chi2UseVertex_, chi2FirstMomentum_) : 0;
        if (thisChi2 >= maxChi2_) return false;
        switch (sortBy_) {
            case LocalPosDiff:      isBest = (thisLocalPosDiff      < lastDeltaLocalPos); break;
            case GlobalMomDeltaR:   isBest = (thisGlobalMomDeltaR   < lastDeltaR);        break;
            case GlobalMomDeltaEta: isBest = (thisGlobalMomDeltaEta < lastDeltaEta);      break;
            case GlobalMomDeltaPhi: isBest = (thisGlobalMomDeltaPhi < lastDeltaPhi);      break;
            case GlobalDPtRel:      isBest = (thisGlobalDPtRel      < lastGlobalDPtRel);  break;
            case Chi2:              isBest = (thisChi2              < lastChi2);          break;
        }
        if (isBest) {
            lastDeltaLocalPos = thisLocalPosDiff;
            lastDeltaR        = thisGlobalMomDeltaR;
            lastDeltaEta      = thisGlobalMomDeltaEta;
            lastDeltaPhi      = thisGlobalMomDeltaPhi;
            lastGlobalDPtRel  = thisGlobalDPtRel;
            lastChi2          = thisChi2;
        } 
    }  // if match

    return isBest;
}

double
MatcherUsingTracksAlgorithm::getChi2(const FreeTrajectoryState &start, const FreeTrajectoryState &other, bool diagonalOnly, bool useVertex, bool useFirstMomentum) {
    if (!start.hasError() && !other.hasError()) throw cms::Exception("LogicError") << "At least one of the two states must have errors to make chi2s.\n";
    AlgebraicSymMatrix55 cov;
    if (start.hasError()) cov += start.curvilinearError().matrix();
    if (other.hasError()) cov += other.curvilinearError().matrix();
    cropAndInvert(cov, diagonalOnly, !useVertex);
    GlobalVector p1 = start.momentum(), p2 = other.momentum();
    GlobalPoint  x1 = start.position(), x2 = other.position();
    GlobalVector p = useFirstMomentum ? p1 : p2; double pt = p.perp(), pm = p.mag();
    double dsz = (x1.z()-x2.z())*pt/pm - ( (x1.x()-x2.x())*p.x() + (x1.y()-x2.y())*p.y() ) / pt * p.z()/pm;
    double dxy = ( -(x1.x()-x2.x())*p.y() + (x1.y()-x2.y())*p.x() )/pt;
    AlgebraicVector5 diff(start.charge()/p1.mag()-other.charge()/p2.mag(),
                          p1.theta()-p2.theta(),
                          (p1.phi()-p2.phi()).value(), 
                          dxy,
                          dsz);
    return ROOT::Math::Similarity(diff, cov);
}

double
MatcherUsingTracksAlgorithm::getChi2(const FreeTrajectoryState &start, const TrajectoryStateClosestToPoint &other, bool diagonalOnly, bool useVertex) {
    if (!start.hasError() && !other.hasError()) throw cms::Exception("LogicError") << "At least one of the two states must have errors to make chi2s.\n";
    double pt; // needed by pgconvert
    AlgebraicSymMatrix55 cov;
    if (start.hasError()) cov += PerigeeConversions::ftsToPerigeeError(start).covarianceMatrix();
    if (other.hasError()) cov += other.perigeeError().covarianceMatrix();
    cropAndInvert(cov, diagonalOnly, !useVertex);
    AlgebraicVector5 pgpar1 = PerigeeConversions::ftsToPerigeeParameters(start,other.referencePoint(),pt).vector();
    AlgebraicVector5 pgpar2 = other.perigeeParameters().vector();
    AlgebraicVector5 diff(pgpar1-pgpar2);
    return ROOT::Math::Similarity(diff, cov);
}

double
MatcherUsingTracksAlgorithm::getChi2(const TrajectoryStateOnSurface &start, const TrajectoryStateOnSurface &other, bool diagonalOnly, bool usePosition) {
    if (!start.hasError() && !other.hasError()) throw cms::Exception("LogicError") << "At least one of the two states must have errors to make chi2s.\n";
    AlgebraicSymMatrix55 cov;
    if (start.hasError()) cov += start.localError().matrix();
    if (other.hasError()) cov += other.localError().matrix();
    cropAndInvert(cov, diagonalOnly, !usePosition);
    AlgebraicVector5 diff(start.localParameters().mixedFormatVector() - other.localParameters().mixedFormatVector());
    return ROOT::Math::Similarity(diff, cov);
}

void
MatcherUsingTracksAlgorithm::cropAndInvert(AlgebraicSymMatrix55 &cov, bool diagonalOnly, bool top3by3only) {
    if (!top3by3only) {
        if (diagonalOnly) {
            for (size_t i = 0; i < 5; ++i) { for (size_t j = i+1; j < 5; ++j) {
                cov(i,j) = 0;
            } }
        }
        cov.Invert();
    } else {
        // get 3x3 covariance
        AlgebraicSymMatrix33 momCov = cov.Sub<AlgebraicSymMatrix33>(0,0); // get 3x3 matrix
        if (diagonalOnly) { momCov(0,1) = 0; momCov(0,2) = 0; momCov(1,2) = 0; }
        // invert        
        momCov.Invert();
        // place it
        cov.Place_at(momCov,0,0);
        // zero the rest
        for (size_t i = 3; i < 5; ++i) { for (size_t j = i; j < 5; ++j) { 
            cov(i,j) = 0;
        } }
    }
}