/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_6_2_5/src/RecoVertex/GhostTrackFitter/src/SequentialGhostTrackFitter.cc

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#include <vector>

#include "RecoVertex/GhostTrackFitter/interface/GhostTrackState.h"
#include "RecoVertex/GhostTrackFitter/interface/GhostTrackPrediction.h"

#include "RecoVertex/GhostTrackFitter/interface/SequentialGhostTrackFitter.h"

using namespace reco;

namespace {
        static inline double sqr(double arg) { return arg * arg; }
}

SequentialGhostTrackFitter::SequentialGhostTrackFitter() :
        maxIteration(15),
        minDeltaR(0.0015),
        minDistance(0.002),
        weightThreshold(0.001)
{
}

bool SequentialGhostTrackFitter::stable(
                                const GhostTrackPrediction &before,
                                const GhostTrackPrediction &after) const
{
        return (sqr(after.sz() - before.sz()) +
                sqr(after.ip() - before.ip()) < sqr(minDistance) &&
                sqr(after.eta() - before.eta()) +
                sqr(after.phi() - before.phi()) < sqr(minDeltaR));
}

GhostTrackPrediction SequentialGhostTrackFitter::fit(
                        const GhostTrackFitter::PredictionUpdater &updater,
                        const GhostTrackPrediction &prior,
                        std::vector<GhostTrackState> &states,
                        double &ndof, double &chi2)
{
        GhostTrackPrediction pred, lastPred = prior;

        reset();

        ndof = 0.;
        chi2 = 0.;

        unsigned int iteration = 0;
        for(;;) {
                pred = prior;

                if (states.begin() == states.end())
                        break;

                if (iteration > 0) {
                        for(unsigned int i = 0; i < states.size(); i++) {
                                GhostTrackState &state = states[i];
                                state.linearize(lastPred);
                        }
                }

                ndof = 0.; // prior gives us an initial ndof
                chi2 = 0.;

                for(std::vector<GhostTrackState>::const_iterator state = 
                        states.begin(); state != states.end(); ++state) {

                        if (state->isValid() &&
                            state->weight() > weightThreshold)
                                pred = updater.update(pred, *state,
                                                      ndof, chi2);
                }

                if (++iteration >= maxIteration || stable(lastPred, pred))
                        break;

                postFit(updater, pred, states);

                lastPred = pred;
        }

        return pred;
}