FitParameters.cxx

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/
 
/***************************************************************************
 local parameter values used during fitter
 ***************************************************************************/
 
#include "TrkiPatFitterUtils/FitParameters.h"
 
#include <cmath>
#include <iomanip>
#include <iostream>
 
#include "GaudiKernel/MsgStream.h"
#include "GaudiKernel/SystemOfUnits.h"
#include "TrkEventPrimitives/ParamDefs.h"
#include "TrkExUtils/TrackSurfaceIntersection.h"
#include "TrkMaterialOnTrack/ScatteringAngles.h"
#include "TrkSurfaces/Surface.h"
#include "TrkiPatFitterUtils/ExtrapolationType.h"
#include "TrkiPatFitterUtils/ParameterType.h"
 
namespace Trk {
 
FitParameters::FitParameters(const Perigee& perigee)
    : m_cosPhi1(0.),
      m_cosTheta1(0.),
      m_d0(perigee.parameters()[Trk::d0]),
      m_differences{},
      m_extremeMomentum(false),
      m_finalCovariance(nullptr),
      m_firstAlignmentParameter(0),
      m_firstScatteringParameter(0),
      m_fitEnergyDeposit(false),
      m_fitMomentum(true),
      m_fullCovariance(nullptr),
      m_minEnergyDeposit(0.),
      m_numberAlignments(0),
      m_numberOscillations(0),
      m_numberParameters(0),
      m_numberScatterers(0),
      m_oldDifference(0.),
      m_perigee(&perigee),
      m_phiInstability(false),
      m_qOverP1(0.),
      m_sinPhi1(0.),
      m_sinTheta1(0.),
      m_surface(&perigee.associatedSurface()),
      m_vertex(perigee.associatedSurface().center()),
      m_z0(perigee.position().z()) {
  Amg::Vector3D momentum = perigee.momentum();
  const double ptInv0 = 1. / momentum.perp();
  m_cosPhi = ptInv0 * momentum.x();
  m_sinPhi = ptInv0 * momentum.y();
  m_cotTheta = ptInv0 * momentum.z();
  m_sinTheta = 1. / std::sqrt(1. + m_cotTheta * m_cotTheta);
  m_cosTheta = m_cotTheta * m_sinTheta;
  m_qOverP = perigee.charge() * ptInv0 * m_sinTheta;
  m_position = Amg::Vector3D(m_vertex.x() - m_d0 * m_sinPhi,
                             m_vertex.y() + m_d0 * m_cosPhi, m_z0);
}
 
FitParameters::FitParameters(double d0, double z0, double cosPhi, double sinPhi,
                             double cotTheta, double ptInv0,
                             const PerigeeSurface& surface)
    : m_cosPhi(cosPhi),
      m_cosPhi1(0.),
      m_cosTheta1(0.),
      m_cotTheta(cotTheta),
      m_d0(d0),
      m_extremeMomentum(false),
      m_finalCovariance(nullptr),
      m_firstAlignmentParameter(0),
      m_firstScatteringParameter(0),
      m_fitEnergyDeposit(false),
      m_fitMomentum(true),
      m_fullCovariance(nullptr),
      m_minEnergyDeposit(0.),
      m_numberAlignments(0),
      m_numberOscillations(0),
      m_numberParameters(0),
      m_numberScatterers(0),
      m_oldDifference(0.),
      m_perigee(nullptr),
      m_phiInstability(false),
      m_qOverP1(0.),
      m_sinPhi(sinPhi),
      m_sinPhi1(0.),
      m_sinTheta1(0.),
      m_surface(&surface),
      m_vertex(surface.center()),
      m_z0(z0) {
  m_sinTheta = 1. / std::sqrt(1. + m_cotTheta * m_cotTheta);
  m_cosTheta = m_cotTheta * m_sinTheta;
  m_qOverP = ptInv0 * m_sinTheta;
  m_z0 = z0;
  m_position = Amg::Vector3D(m_vertex.x() - m_d0 * m_sinPhi,
                             m_vertex.y() + m_d0 * m_cosPhi, m_z0);
}
 
 
void FitParameters::addAlignment(bool constrained, double angle,
                                 double offset) {
  m_alignmentAngle[m_numberAlignments] = angle;
  m_alignmentOffset[m_numberAlignments] = offset;
  if (constrained) {
    m_alignmentAngleConstraint[m_numberAlignments] = angle;
    m_alignmentOffsetConstraint[m_numberAlignments] = offset;
  }
  ++m_numberAlignments;
}
 
void FitParameters::addScatterer(double phi, double theta) {
  m_scattererPhi[m_numberScatterers] = phi;
  m_scattererTheta[m_numberScatterers] = theta;
  ++m_numberScatterers;
}
 
const Surface* FitParameters::associatedSurface(void) const {
  if (!m_perigee)
    return nullptr;
  return &m_perigee->associatedSurface();
}
 
void FitParameters::covariance(Amg::MatrixX* finalCovariance,
                               const Amg::MatrixX* fullCovariance) {
  m_finalCovariance = finalCovariance;
  m_fullCovariance = fullCovariance;
}
 
void FitParameters::d0(double value) {
  m_d0 = value;
  m_position = Amg::Vector3D(m_vertex.x() - m_d0 * m_sinPhi,
                             m_vertex.y() + m_d0 * m_cosPhi, m_z0);
}
 
void FitParameters::extremeMomentum(bool value) {
  m_extremeMomentum = value;
  m_fitEnergyDeposit = !value;
}
 
void FitParameters::fitEnergyDeposit(double minEnergyDeposit) {
  m_fitEnergyDeposit = true;
  m_minEnergyDeposit = minEnergyDeposit;
}
 
void FitParameters::fitMomentum(bool value) {
  m_fitMomentum = value;
}
 
TrackSurfaceIntersection FitParameters::intersection(void) const {
  return TrackSurfaceIntersection(
      m_position,
      Amg::Vector3D(m_cosPhi * m_sinTheta, m_sinPhi * m_sinTheta, m_cosTheta),
      0.);
}
 
void FitParameters::numberAlignments(int numberAlignments) {
  m_numberAlignments = 0;
  if (!numberAlignments)
    return;
  m_alignmentAngle = std::vector<double>(numberAlignments, 0.);
  m_alignmentAngleConstraint = std::vector<double>(numberAlignments, 0.);
  m_alignmentOffset = std::vector<double>(numberAlignments, 0.);
  m_alignmentOffsetConstraint = std::vector<double>(numberAlignments, 0.);
}
 
void FitParameters::numberParameters(int numberParameters) {
  m_numberParameters = numberParameters;
  m_firstAlignmentParameter = numberParameters - 2 * m_numberAlignments - 1;
  m_firstScatteringParameter =
      m_firstAlignmentParameter - 2 * m_numberScatterers;
}
 
void FitParameters::numberScatterers(int numberScatterers) {
  m_numberScatterers = 0;
  if (!numberScatterers)
    return;
  m_scattererPhi = std::vector<double>(numberScatterers, 0.);
  m_scattererTheta = std::vector<double>(numberScatterers, 0.);
}
 
const Amg::MatrixX FitParameters::parameterDifference(
    const Amg::VectorX& parameters) const {
  Amg::MatrixX difference(1, 5);
  difference(0, 0) = parameters(0) - m_d0;
  difference(0, 1) = parameters(1) - m_z0;
  difference(0, 2) = parameters(3) * m_cosPhi - parameters(2) * m_sinPhi;
 
  // FIXME: diff is now delta(theta) : check sign
  // difference[0][3] = parameters[4] - m_cotTheta;
  difference(0, 3) = std::sin(parameters(4)) * m_cosTheta -
                     std::cos(parameters(4)) * m_sinTheta;
  difference(0, 4) = (parameters(5) - m_qOverP) * Gaudi::Units::TeV;
  return difference;
}
 
void FitParameters::performCutStep(double cutStep) {
  // revert parameters to previous parameter change with cutStep*value
  // i.e. 0 < cutstep < 1 such that cutStep = 0 gives complete reversion
 
  Amg::VectorX cutDifferences(m_differences);
  cutDifferences *= (cutStep - 1.);
  Amg::VectorX oldDifferences(m_differences);
  oldDifferences *= cutStep;
 
  // leave phi alone when unstable
  if (m_phiInstability) {
    cutDifferences(2) = 0.;
    oldDifferences(2) = (m_differences)(2);
  }
 
  // apply cut
  update(cutDifferences);
  m_differences = Amg::VectorX(std::move(oldDifferences));
 
  m_numberOscillations = 0;
  m_oldDifference = 0.;
}
 
Perigee* FitParameters::perigee(void) const {
  // copy 'final' covariance
  AmgSymMatrix(5) covMatrix = AmgSymMatrix(5)(*m_finalCovariance);
  const double pT = std::abs(m_sinTheta / m_qOverP);
  double charge = 1.;
  if (m_qOverP < 0.)
    charge = -1.;
  const Amg::Vector3D momentum(pT * m_cosPhi, pT * m_sinPhi, pT * m_cotTheta);
 
  if (m_surface) {
    return new Perigee(m_position, momentum, charge,
                       dynamic_cast<const Trk::PerigeeSurface&>(*m_surface),
                       std::move(covMatrix));
  } else {
    return new Perigee(m_position, momentum, charge, m_vertex,
                       std::move(covMatrix));
  }
}
 
bool FitParameters::phiInstability(void) const {
  return m_phiInstability;
}
 
void FitParameters::print(MsgStream& log) const {
  log << std::setiosflags(std::ios::fixed | std::ios::right) << std::setw(16)
      << std::setprecision(1) << m_position.perp() << " perigee radius"
      << std::setw(10) << std::setprecision(3) << m_d0 << " d0" << std::setw(11)
      << std::setprecision(3) << m_position.z() << " z0" << std::setw(11)
      << std::setprecision(6) << std::atan2(m_sinPhi, m_cosPhi) << " phi"
      << std::setw(11) << std::setprecision(6) << std::acos(m_cosTheta)
      << " theta" << std::setw(13) << std::setprecision(3)
      << m_sinTheta / (m_qOverP * Gaudi::Units::GeV) << " pT (GeV)";
}
 
void FitParameters::printCovariance(MsgStream& log) const {
  double error00 = 0.;
  const Amg::MatrixX& cov = *m_finalCovariance;
  if (cov(0, 0) > 0.)
    error00 = std::sqrt(cov(0, 0));
  double error11 = 0.;
  if (cov(1, 1) > 0.)
    error11 = std::sqrt(cov(1, 1));
  double error22 = 0.;
  if (cov(2, 2) > 0.)
    error22 = std::sqrt(cov(2, 2));
  double error33 = 0.;
  if (cov(3, 3) > 0.)
    error33 = std::sqrt(cov(3, 3));
  double error44 = 0.;
  if (cov(4, 4) > 0.)
    error44 = std::sqrt(cov(4, 4));
  double correl02 = 0.;
  const double denom02 = cov(0, 0) * cov(2, 2);
  if (denom02 > 0.)
    correl02 = cov(0, 2) / std::sqrt(denom02);
  double correl13 = 0.;
  const double denom13 = cov(1, 1) * cov(3, 3);
  if (denom13 > 0.)
    correl13 = cov(1, 3) / std::sqrt(denom13);
  log << std::setiosflags(std::ios::fixed | std::ios::right) << std::setw(10)
      << std::setprecision(3) << error00 << std::setw(14)
      << std::setprecision(3) << error11 << std::setw(14)
      << std::setprecision(6) << error22 << std::setw(15)
      << std::setprecision(6) << error33 << std::setw(19)
      << std::setprecision(3)
      << (error44 * m_sinTheta) / (m_qOverP * m_qOverP * Gaudi::Units::GeV)
      << " (covariance)" << std::setw(9) << std::setprecision(3) << correl02
      << " Cd0phi" << std::setw(8) << std::setprecision(3) << correl13
      << " Cz0theta" << std::endl;
}
 
void FitParameters::printVerbose(MsgStream& log) const {
  log << std::endl;
 
  if (m_differences.size() != 0) {
    const Amg::VectorX& differences = m_differences;
    log << "      dParams ====" << std::setiosflags(std::ios::fixed)
        << std::setw(10) << std::setprecision(4) << differences(0) << " (0) "
        << std::setw(10) << std::setprecision(4) << differences(1) << " (1) "
        << std::setw(10) << std::setprecision(5) << differences(2) << " (2) "
        << std::setw(10) << std::setprecision(5) << differences(3) << " (3) "
        << std::setw(13) << std::setprecision(9)
        << differences(4) * Gaudi::Units::GeV / Gaudi::Units::TeV << " (4) ";
    if (m_fitEnergyDeposit)
      log << std::setiosflags(std::ios::fixed) << std::setw(13)
          << std::setprecision(9)
          << differences(5) * Gaudi::Units::GeV / Gaudi::Units::TeV << " (5) ";
    log << std::endl;
 
    if (m_numberAlignments) {
      log << "       dAlign ==== ";
      unsigned param = m_firstAlignmentParameter;
      for (int scat = 0; scat < m_numberAlignments; ++scat) {
        ++param;
        if (scat % 5 == 0 && scat > 0)
          log << std::endl << "                   ";
        log << std::setiosflags(std::ios::fixed) << std::setw(10)
            << std::setprecision(6) << differences(param);
        ++param;
        log << std::setiosflags(std::ios::fixed) << std::setw(10)
            << std::setprecision(6) << differences(param) << " ("
            << std::setw(2) << scat << "A)     ";
      }
      log << std::endl;
    }
 
    if (m_numberScatterers) {
      log << "        dScat ==== ";
      unsigned param = m_firstScatteringParameter;
      for (int scat = 0; scat < m_numberScatterers; ++scat) {
        ++param;
        if (scat % 5 == 0 && scat > 0)
          log << std::endl << "                   ";
        log << std::setiosflags(std::ios::fixed) << std::setw(10)
            << std::setprecision(6) << differences(param);
        ++param;
        log << std::setiosflags(std::ios::fixed) << std::setw(10)
            << std::setprecision(6) << differences(param) << " ("
            << std::setw(2) << scat << "S)     ";
      }
      log << std::endl;
    }
  }
 
  log << std::setiosflags(std::ios::fixed | std::ios::right)
      << "   parameters:   " << std::setw(12) << std::setprecision(4) << m_d0
      << " transverse impact  " << std::setw(10) << std::setprecision(4)
      << m_position.z() << " z0  " << std::setw(10) << std::setprecision(6)
      << std::atan2(m_sinPhi, m_cosPhi) << std::setw(10) << std::setprecision(6)
      << m_cotTheta << " phi,cotTheta  " << std::setw(13)
      << std::setprecision(9) << m_qOverP / m_sinTheta << " inverse pT  "
      << std::setw(12) << std::setprecision(6)
      << m_sinTheta / (m_qOverP * Gaudi::Units::GeV) << " signed pT  ";
  if (m_fitEnergyDeposit) {
    // TODO: should give fitted energy loss
    log << std::endl
        << "    E before/after energy deposit" << std::setw(12)
        << std::setprecision(3) << 1. / std::abs(m_qOverP * Gaudi::Units::GeV)
        << std::setw(12) << std::setprecision(3)
        << 1. / std::abs(m_qOverP1 * Gaudi::Units::GeV);
  }
  if (m_numberAlignments) {
    log << std::endl << "   alignment number, angle, offset:  ";
    for (int align = 0; align < m_numberAlignments; ++align) {
      log << std::setiosflags(std::ios::fixed) << std::setw(6) << align
          << std::setw(10) << std::setprecision(6) << m_alignmentAngle[align]
          << std::setw(10) << std::setprecision(6) << m_alignmentOffset[align];
      if ((align + 1) % 5 == 0)
        log << std::endl << "                                                ";
    }
  }
  if (m_numberScatterers) {
    log << std::endl << "   scatterer number, delta(phi), delta(theta):  ";
    for (int scat = 0; scat < m_numberScatterers; ++scat) {
      log << std::setiosflags(std::ios::fixed) << std::setw(6) << scat
          << std::setw(10) << std::setprecision(6) << m_scattererPhi[scat]
          << std::setw(10) << std::setprecision(6) << m_scattererTheta[scat];
      if ((scat + 1) % 5 == 0)
        log << std::endl << "                                                ";
    }
  }
  log << std::endl;
}
 
void FitParameters::qOverP(double value) {
  m_qOverP = value;
}
 
void FitParameters::qOverP1(double value) {
  m_qOverP1 = value;
}
 
void FitParameters::reset(const FitParameters& parameters) {
  // method is needed to complement copy in places where design uses
  // a reference to a FitParameter pointer
  // essentially a copy, with history of previous iteration removed
  m_cosPhi = parameters.m_cosPhi;
  m_cosPhi1 = parameters.m_cosPhi1;
  m_cosTheta = parameters.m_cosTheta;
  m_cosTheta1 = parameters.m_cosTheta1;
  m_cotTheta = parameters.m_cotTheta;
  m_d0 = parameters.m_d0;
  m_extremeMomentum = parameters.m_extremeMomentum;
  m_finalCovariance = parameters.m_finalCovariance;
  m_firstScatteringParameter = parameters.m_firstScatteringParameter;
  m_firstScatteringParameter = parameters.m_firstScatteringParameter;
  m_fitEnergyDeposit = parameters.m_fitEnergyDeposit;
  m_fitMomentum = parameters.m_fitMomentum;
  m_fullCovariance = parameters.m_fullCovariance;
  m_minEnergyDeposit = parameters.m_minEnergyDeposit;
  m_numberAlignments = parameters.m_numberAlignments;
  m_numberOscillations = parameters.m_numberOscillations;
  m_numberParameters = parameters.m_numberParameters;
  m_numberScatterers = parameters.m_numberScatterers;
  m_oldDifference = parameters.m_oldDifference;
  m_perigee = parameters.m_perigee;
  m_phiInstability = parameters.m_phiInstability;
  m_position = parameters.m_position;
  m_qOverP = parameters.m_qOverP;
  m_qOverP1 = parameters.m_qOverP1;
  m_sinPhi = parameters.m_sinPhi;
  m_sinPhi1 = parameters.m_sinPhi1;
  m_sinTheta = parameters.m_sinTheta;
  m_sinTheta1 = parameters.m_sinTheta1;
  m_vertex = parameters.vertex();
  m_z0 = parameters.m_z0;
  for (int s = 0; s != m_numberAlignments; ++s) {
    m_alignmentAngle[s] = parameters.m_alignmentAngle[s];
    m_alignmentAngleConstraint[s] = parameters.m_alignmentAngleConstraint[s];
    m_alignmentOffset[s] = parameters.m_alignmentOffset[s];
    m_alignmentOffsetConstraint[s] = parameters.m_alignmentOffsetConstraint[s];
  }
  for (int s = 0; s != m_numberScatterers; ++s) {
    m_scattererPhi[s] = parameters.m_scattererPhi[s];
    m_scattererTheta[s] = parameters.m_scattererTheta[s];
  }
 
  // restore difference history
  if (parameters.m_differences.size() != 0) {
    m_differences = Amg::VectorX(parameters.m_differences);
  } else {
    m_differences = Amg::VectorX(m_numberParameters);
    m_differences.setZero();
  }
 
  m_numberOscillations = 0;
  m_oldDifference = 0.;
}
 
ScatteringAngles FitParameters::scatteringAngles(
    const FitMeasurement& fitMeasurement, int scatterer) const {
  // scattering sigma used in chi2 computation
  const double scattererSigmaTheta = 1. / fitMeasurement.weight();
  const double scattererSigmaPhi =
      scattererSigmaTheta /
      fitMeasurement.intersection(FittedTrajectory).direction().perp();
  if (scatterer < 0) {
    return {0., 0., scattererSigmaPhi, scattererSigmaTheta};
  } else {
    return {m_scattererPhi[scatterer], m_scattererTheta[scatterer],
            scattererSigmaPhi, scattererSigmaTheta};
  }
}
 
void FitParameters::setPhiInstability(void) {
  m_phiInstability = true;
}
 
Perigee* FitParameters::startingPerigee(void) const {
  // create momentum
  const double pT = std::abs(m_sinTheta / m_qOverP);
  double charge = 1.;
  if (m_qOverP < 0.)
    charge = -1.;
  const Amg::Vector3D momentum(pT * m_cosPhi, pT * m_sinPhi, pT * m_cotTheta);
 
  return new Perigee(m_position, momentum, charge, m_vertex);
}
 
TrackParameters* FitParameters::trackParameters(
    MsgStream& log, const FitMeasurement& measurement, bool withCovariance) {
  // make checks necessary for the TrackParameters to be computed
  //   1) a Surface is required
  if (!measurement.surface()) {
    log << MSG::WARNING
        << "FitParameters::trackParameters - measurement lacks Surface"
        << endmsg;
    return nullptr;
  }
 
  //   2) a SurfaceIntersection is required
  if (!measurement.hasIntersection(FittedTrajectory)) {
    log << MSG::WARNING
        << "FitParameters::trackParameters - invalid measurement" << endmsg;
    return nullptr;
  }
 
  //   3) the intersection position has to lie sufficiently close to the Surface
  const TrackSurfaceIntersection& intersection =
      measurement.intersection(FittedTrajectory);
  Amg::Vector2D localPos;
  if (!measurement.surface()->globalToLocal(
          intersection.position(), intersection.direction(), localPos)) {
    log << MSG::WARNING
        << "FitParameters::trackParameters - globalToLocal failure" << endmsg;
    return nullptr;
  }
 
  // cache parameters at EnergyDeposit
  if (measurement.isEnergyDeposit()) {
    m_sinTheta1 = intersection.direction().perp();
    m_cosPhi1 = intersection.direction().x() / m_sinTheta1;
    m_sinPhi1 = intersection.direction().y() / m_sinTheta1;
    m_cosTheta1 = intersection.direction().z();
    m_qOverP1 = measurement.qOverP();
  }
 
  // propagate full covariance to form localCovariance
  std::optional<AmgSymMatrix(5)> covMatrix = std::nullopt;
  if (withCovariance && (measurement.isDrift() || measurement.isCluster() ||
                         measurement.isPerigee())) {
    Amg::Vector3D direction = intersection.direction();
    const double sigma = 1. / measurement.weight();
    const double sigma2 = 1. / measurement.weight2();
    int const lastParameter = measurement.lastParameter();
    Amg::MatrixX jacobian = Amg::MatrixX::Zero(5, lastParameter);
    for (int i = 0; i != lastParameter; ++i) {
      jacobian(0, i) = sigma * measurement.derivative(i);
      jacobian(1, i) = sigma2 * measurement.derivative2(i);
    }
 
    // phi,theta derivs into jac
    jacobian(2, 2) = 1.;
    jacobian(3, 3) = 1.;
    int i = m_firstScatteringParameter;
    while (++i < lastParameter) {
      jacobian(2, i) = 1.;
      ++i;
      jacobian(3, i) = 1.;
    }
 
    // only if fit to curvature
    if (m_fitMomentum && m_qOverP) {
      const double sinTheta = direction.perp();
      if (m_fitEnergyDeposit && measurement.afterCalo()) {
        const double deltaPhi =
            (direction.y() * m_cosPhi1 - direction.x() * m_sinPhi1) / sinTheta;
        const double deltaTheta =
            (sinTheta * m_cosTheta1 - direction.z() * m_sinTheta1);
        jacobian(0, 5) *= Gaudi::Units::TeV;
        jacobian(1, 5) *= Gaudi::Units::TeV;
        jacobian(2, 5) = deltaPhi / measurement.qOverP();
        jacobian(3, 5) = deltaTheta / measurement.qOverP();
        jacobian(4, 5) = measurement.qOverP() / m_qOverP1;
      } else {
        const double deltaPhi =
            (direction.y() * m_cosPhi - direction.x() * m_sinPhi) / sinTheta;
        const double deltaTheta =
            (sinTheta * m_cosTheta - direction.z() * m_sinTheta);
        jacobian(0, 4) *= Gaudi::Units::TeV;
        jacobian(1, 4) *= Gaudi::Units::TeV;
        jacobian(2, 4) = deltaPhi / measurement.qOverP();
        jacobian(3, 4) = deltaTheta / measurement.qOverP();
        jacobian(4, 4) = measurement.qOverP() / m_qOverP;
      }
    } else {
      jacobian(4, 4) = 1.;
    }
 
    // similarity transform
    covMatrix = AmgSymMatrix(5)(
        jacobian * m_fullCovariance->block(0, 0, lastParameter, lastParameter) *
        jacobian.transpose());
  }
 
  double phi = intersection.direction().phi();
  double theta = intersection.direction().theta();
  if (measurement.isFlipped()) {
    if (phi > 0.) {
      phi -= M_PI;
    } else {
      phi += M_PI;
    }
    theta = M_PI - theta;
  }
 
  if (!measurement.surface()) {
    log << MSG::WARNING
        << "FitParameters::trackParameters - unrecognized surface" << endmsg;
    return nullptr;
  }
  // finally can create the appropriate TrackParameters based on the surface
  return measurement.surface()
      ->createUniqueTrackParameters(localPos[locR], localPos[locZ], phi, theta,
                                    measurement.qOverP(), std::move(covMatrix))
      .release();
}
 
void FitParameters::update(const Amg::VectorX& differences) {
  // keep update values in case of cutStep procedure
  if (m_numberOscillations && m_oldDifference * differences(4) < 0.) {
    ++m_numberOscillations;
  } else {
    m_numberOscillations = 1;
  }
  m_differences = Amg::VectorX(differences);
  m_oldDifference = differences(4);
 
  // misalignment parameters
  std::vector<double>::iterator a = m_alignmentAngle.begin();
  std::vector<double>::iterator o = m_alignmentOffset.begin();
  int align = m_firstAlignmentParameter;
  for (int i = 0; i != m_numberAlignments; ++i) {
    (*a++) += differences(++align);
    (*o++) += differences(++align);
  }
 
  // scattering angles
  std::vector<double>::iterator p = m_scattererPhi.begin();
  std::vector<double>::iterator t = m_scattererTheta.begin();
  int scat = m_firstScatteringParameter;
  for (int i = 0; i != m_numberScatterers; ++i) {
    (*p++) += differences(++scat);
    (*t++) += differences(++scat);
  }
 
  // qOverP, cotTheta
  if (m_fitMomentum)
    m_qOverP += differences(4) / Gaudi::Units::TeV;
  m_cotTheta -= differences(3) / (m_sinTheta * m_sinTheta);
 
  // impose charge conservation and decreasing energy
  if (m_fitEnergyDeposit) {
    m_qOverP1 += differences(5) / Gaudi::Units::TeV;
    const double deposit = 1. / std::abs(m_qOverP) - 1. / std::abs(m_qOverP1);
    if (std::abs(deposit) < std::abs(m_minEnergyDeposit) ||
        deposit * m_minEnergyDeposit < 0. || m_qOverP * m_qOverP1 < 0.) {
      m_qOverP = 1. / (1. / std::abs(m_qOverP1) + m_minEnergyDeposit);
      if (m_qOverP1 < 0.)
        m_qOverP = -m_qOverP;
    }
  }
 
  // protect phi against some rounding instabilities
  double sinDPhi = differences(2);
  double cosDPhi = 0.;
  if (std::abs(sinDPhi) < 1.0) {
    cosDPhi = std::sqrt(1. - sinDPhi * sinDPhi);
  } else {
    if (sinDPhi > 0.) {
      sinDPhi = 1.0;
    } else {
      sinDPhi = -1.0;
    }
  }
 
  const double cosPhi = m_cosPhi * cosDPhi - m_sinPhi * sinDPhi;
  m_sinPhi = m_sinPhi * cosDPhi + m_cosPhi * sinDPhi;
  m_cosPhi = cosPhi;
  m_z0 += differences(1);
  m_d0 += differences(0);
  m_sinTheta = 1. / std::sqrt(1. + m_cotTheta * m_cotTheta);
  m_cosTheta = m_cotTheta * m_sinTheta;
  m_position = Amg::Vector3D(m_vertex.x() - m_d0 * m_sinPhi,
                             m_vertex.y() + m_d0 * m_cosPhi, m_z0);
}
 
void FitParameters::update(Amg::Vector3D position, Amg::Vector3D direction,
                           double qOverP,
                           const Amg::MatrixX& leadingCovariance) {
  // update parameters after leading material corrections
  m_position = position;
  m_sinTheta = direction.perp();
  const double sinThetaInv = 1. / m_sinTheta;
  m_cotTheta = sinThetaInv * m_cosTheta;
  m_cosPhi = sinThetaInv * direction.x();
  m_sinPhi = sinThetaInv * direction.y();
  m_cotTheta = sinThetaInv * direction.z();
  m_cosTheta = direction.z();
  m_qOverP = qOverP;
  m_z0 = position.z();
  m_d0 = (m_vertex.x() - position.x()) * m_sinPhi -
         (m_vertex.y() - position.y()) * m_cosPhi;
 
  // update covariance
  // (*m_finalCovariance) += leadingCovariance; // ??
  for (int i = 0; i != 5; ++i) {
    for (int j = 0; j != 5; ++j) {
      (*m_finalCovariance)(i, j) += leadingCovariance(i, j);
    }
  }
}
 
}  // namespace Trk