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 {
#ifndef __clang__
  static inline double sqr(double arg) { return arg * arg; }
#endif
  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

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_);
}