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_);
}