/data/refman/pasoursint/CMSSW_6_1_2_SLHC4_patch1/src/RecoVertex/GhostTrackFitter/src/VertexGhostTrackState.cc

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#include <cmath>

#include <Math/SMatrix.h>
#include <Math/MatrixFunctions.h>

#include "DataFormats/GeometryVector/interface/GlobalPoint.h"
#include "DataFormats/GeometryVector/interface/GlobalVector.h"

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

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

using namespace reco;

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

        using namespace ROOT::Math;

        typedef SVector<double, 3> Vector3;

        typedef SMatrix<double, 3, 3, MatRepSym<double, 3> > Matrix3S;
        typedef SMatrix<double, 6, 6, MatRepSym<double, 6> > Matrix6S;
        typedef SMatrix<double, 3, 3> Matrix33;
        typedef SMatrix<double, 3, 6> Matrix36;

        static inline Vector3 conv(const GlobalVector &vec)
        {
                Vector3 result;
                result[0] = vec.x();
                result[1] = vec.y();
                result[2] = vec.z();
                return result;
        }
}

BasicGhostTrackState::Vertex VertexGhostTrackState::vertexStateOnGhostTrack(
        const GhostTrackPrediction &pred, bool withMeasurementError) const
{
        using namespace ROOT::Math;

        GlobalPoint origin = pred.origin();
        GlobalVector direction = pred.direction();

        double rho2 = pred.rho2();
        double rho = std::sqrt(rho2);
        double lambda = (position_ - origin) * direction / rho2;
        GlobalPoint pos = origin + lambda * direction;

        Vector3 b = conv(direction) / rho;
        Vector3 ca = conv(position_ - pos);

        Matrix33 pA = TensorProd(b, b);
        Matrix33 pB = TensorProd(b, ca);

        Matrix36 jacobian;
        jacobian.Place_at(-pA + Matrix33(SMatrixIdentity()), 0, 0);
        jacobian.Place_at(pB / rho, 0, 3);
        Matrix3S error = Similarity(jacobian, pred.cartesianError(lambda));

        if (withMeasurementError)
                error += Similarity(pA, covariance_);

        return Vertex(pos, error);
}

BasicGhostTrackState::Vertex VertexGhostTrackState::vertexStateOnMeasurement(
        const GhostTrackPrediction &pred, bool withGhostTrackError) const
{
        return Vertex(position_, covariance_);
}