TrackGhostTrackState.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 "DataFormats/GeometrySurface/interface/Line.h"

#include "TrackingTools/TransientTrack/interface/TransientTrack.h"
#include "TrackingTools/GeomPropagators/interface/AnalyticalImpactPointExtrapolator.h"
#include "TrackingTools/GeomPropagators/interface/AnalyticalTrajectoryExtrapolatorToLine.h"
#include "TrackingTools/TrajectoryState/interface/TrajectoryStateOnSurface.h"
#include "TrackingTools/TrajectoryParametrization/interface/CartesianTrajectoryError.h"

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

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

using namespace reco;

namespace {
  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;

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

bool TrackGhostTrackState::linearize(const GhostTrackPrediction &pred, bool initial, double lambda) {
  AnalyticalTrajectoryExtrapolatorToLine extrap(track_.field());

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

  if (isValid() && !initial) {
    GlobalPoint pca = origin + lambda_ * direction;
    Line line(pca, direction);
    tsos_ = extrap.extrapolate(tsos_, line);
  } else {
    GlobalPoint pca = origin + lambda * direction;
    Line line(pca, direction);
    tsos_ = extrap.extrapolate(track_.impactPointState(), line);
  }

  if (!isValid())
    return false;

  lambda_ = (tsos_.globalPosition() - origin) * direction / pred.rho2();

  return true;
}

bool TrackGhostTrackState::linearize(const GhostTrackPrediction &pred, double lambda) {
  AnalyticalImpactPointExtrapolator extrap(track_.field());

  GlobalPoint point = pred.position(lambda);

  tsos_ = extrap.extrapolate(track_.impactPointState(), point);
  if (!isValid())
    return false;

  lambda_ = lambda;

  return true;
}

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

  if (!isValid())
    return Vertex();

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

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

  GlobalVector momentum = tsos_.globalMomentum();
  double mom = momentum.mag();

  Vector3 b = conv(direction) / rho;
  Vector3 d = conv(momentum) / mom;
  double l = Dot(b, d);
  double g = 1. / (1. - sqr(l));

  Vector3 ca = conv(pos - tsos_.globalPosition());
  Vector3 bd = b - l * d;
  b *= g;

  Matrix33 pA = TensorProd(b, bd);
  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) {
    jacobian.Place_at(pA, 0, 0);
    jacobian.Place_at(-pB / mom, 0, 3);
    error += Similarity(jacobian, tsos_.cartesianError().matrix());
  }

  return Vertex(pos, error);
}

BasicGhostTrackState::Vertex TrackGhostTrackState::vertexStateOnMeasurement(const GhostTrackPrediction &pred,
                                                                            bool withGhostTrackError) const {
  using namespace ROOT::Math;

  if (!isValid())
    return Vertex();

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

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

  GlobalVector momentum = tsos_.globalMomentum();
  double mom = momentum.mag();

  Vector3 b = conv(direction) / rho;
  Vector3 d = conv(momentum) / mom;
  double l = Dot(b, d);
  double g = 1. / (1. - sqr(l));

  Vector3 ca = conv(tsos_.globalPosition() - pos);
  Vector3 bd = l * b - d;
  d *= g;

  Matrix33 pC = TensorProd(d, bd);
  Matrix33 pD = TensorProd(d, ca);

  Matrix36 jacobian;
  jacobian.Place_at(pC + Matrix33(SMatrixIdentity()), 0, 0);
  jacobian.Place_at(pD / mom, 0, 3);
  Matrix3S error = Similarity(jacobian, tsos_.cartesianError().matrix());

  if (withGhostTrackError) {
    jacobian.Place_at(-pC, 0, 0);
    jacobian.Place_at(-pD / rho, 0, 3);
    error += Similarity(jacobian, pred.cartesianError(lambda));
  }

  return Vertex(tsos_.globalPosition(), error);
}