STEP_Propagator.cxx

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/*
  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
*/
 
// Implementation file for class Trk::STEP_Propagator
// (c) ATLAS Detector software
// Based on RungeKuttaPropagator Version 1.0 21/05/2004 I.Gavrilenko
// Version 0.1 16/2/2005 Esben Lund
// Version 1.0 27/7/2006 Esben Lund
 
#include "TrkExSTEP_Propagator/STEP_Propagator.h"
//
#include "TrkDetDescrUtils/BinUtility.h"
#include "TrkEventPrimitives/ParamDefs.h"
#include "TrkEventPrimitives/ParticleHypothesis.h"
 
#include "TrkExInterfaces/ITimedMatEffUpdator.h"
#include "TrkExUtils/ExtrapolationCache.h"
#include "TrkExUtils/RungeKuttaUtils.h"
#include "TrkExUtils/TrackSurfaceIntersection.h"
#include "TrkEventPrimitives/TransportJacobian.h"
#include "TrkGeometry/AlignableTrackingVolume.h"
#include "TrkGeometry/BinnedMaterial.h"
#include "TrkGeometry/MagneticFieldProperties.h"
#include "TrkMaterialOnTrack/MaterialEffectsOnTrack.h"
#include "TrkMaterialOnTrack/ScatteringAngles.h"
#include "TrkSurfaces/Surface.h"
#include "TrkTrack/TrackStateOnSurface.h"
#include "AthenaKernel/RNGWrapper.h"
// CLHEP
#include "CLHEP/Random/RandFlat.h"
#include "CLHEP/Random/RandGauss.h"
#include "GaudiKernel/PhysicalConstants.h"
// Gaudi
#include "EventPrimitives/EventPrimitives.h"
#include "EventPrimitives/EventPrimitivesHelpers.h"
#include "EventPrimitives/EventPrimitivesCovarianceHelpers.h"
#include "EventPrimitives/EventPrimitivesToStringConverter.h"
//
#include <cmath>
 
#include "CxxUtils/vectorize.h"
ATH_ENABLE_VECTORIZATION;
 
#include "CxxUtils/inline_hints.h"
 
 
 
namespace{
 
using Cache = Trk::STEP_Propagator::Cache;
// methods for magnetic field information
void
getField(Cache& cache, const double* ATH_RESTRICT R, double* ATH_RESTRICT H)
{
  if (cache.m_solenoid) {
    cache.m_fieldCache.getFieldZR(R, H);
  } else {
    cache.m_fieldCache.getField(R, H);
  }
}
 
void
getFieldGradient(Cache& cache, const double* ATH_RESTRICT R, double* ATH_RESTRICT H, double* ATH_RESTRICT dH)
{
  if (cache.m_solenoid) {
    cache.m_fieldCache.getFieldZR(R, H, dH);
  } else {
    cache.m_fieldCache.getField(R, H, dH);
  }
}
 
// Get the magnetic field and gradients
// Input: Globalposition
// Output: BG, which contains Bx, By, Bz, dBx/dx, dBx/dy, dBx/dz, dBy/dx,
// dBy/dy, dBy/dz, dBz/dx, dBz/dy, dBz/dz
 
void
getMagneticField(Cache& cache,
                 const Amg::Vector3D& position,
                 bool getGradients,
                 double* ATH_RESTRICT BG)
{
  constexpr double magScale = 10000.;
  const double* R = position.data();
  double H[3];
  double dH[9];
 
  if (getGradients &&
      cache.m_includeBgradients) { // field gradients needed and available
 
    getFieldGradient(cache, R, H, dH);
    BG[0] = H[0] * magScale;
    BG[1] = H[1] * magScale;
    BG[2] = H[2] * magScale;
    BG[3] = dH[0] * magScale;
    BG[4] = dH[1] * magScale;
    BG[5] = dH[2] * magScale;
    BG[6] = dH[3] * magScale;
    BG[7] = dH[4] * magScale;
    BG[8] = dH[5] * magScale;
    BG[9] = dH[6] * magScale;
    BG[10] = dH[7] * magScale;
    BG[11] = dH[8] * magScale;
 
  } else { // Homogenous field or no gradients needed, only retrieve the field
           // strength.
    getField(cache, R, H);
    BG[0] = H[0] * magScale;
    BG[1] = H[1] * magScale;
    BG[2] = H[2] * magScale;
 
    for (int i = 3; i < 12; ++i) { // Set gradients to zero
      BG[i] = 0.;
    }
  }
}
 
// Create straight line in case of q/p = 0
 
std::unique_ptr<Trk::TrackParameters>
createStraightLine(const Trk::TrackParameters* inputTrackParameters)
{
  AmgVector(5) lp = inputTrackParameters->parameters();
  lp[Trk::qOverP] = 1. / 1e10;
 
  if (inputTrackParameters->type() == Trk::Curvilinear) {
    return std::make_unique<Trk::CurvilinearParameters>(
      inputTrackParameters->position(),
      lp[2],
      lp[3],
      lp[4],
      (inputTrackParameters->covariance() ? std::optional<AmgSymMatrix(5)>(*inputTrackParameters->covariance())
                                          : std::nullopt));
  }
  return inputTrackParameters->associatedSurface().createUniqueTrackParameters(
    lp[0],
    lp[1],
    lp[2],
    lp[3],
    lp[4],
    (inputTrackParameters->covariance() ? std::optional<AmgSymMatrix(5)>(*inputTrackParameters->covariance())
                                        : std::nullopt));
}
 
std::unique_ptr<Trk::TrackParameters>
propagateNeutral(const Trk::TrackParameters& parm,
                 std::vector<Trk::DestSurf>& targetSurfaces,
                 Trk::PropDirection propDir,
                 std::vector<unsigned int>& solutions,
                 double& path,
                 bool usePathLimit,
                 bool returnCurv)
{
 
  // find nearest valid intersection
  double tol = 0.001;
  solutions.clear();
  std::vector<std::pair<unsigned int, double>> currentDist;
  currentDist.clear();
  std::vector<std::pair<const Trk::Surface*, Trk::BoundaryCheck>>::iterator sIter = targetSurfaces.begin();
  std::vector<std::pair<unsigned int, double>>::iterator oIter = currentDist.begin();
  std::vector<Trk::DestSurf>::iterator sBeg = targetSurfaces.begin();
 
  const Amg::Vector3D& position(parm.position());
  Amg::Vector3D direction(parm.momentum().normalized());
 
  for (; sIter != targetSurfaces.end(); ++sIter) {
    Trk::DistanceSolution distSol = (*sIter).first->straightLineDistanceEstimate(position, direction);
    if (distSol.numberOfSolutions() > 0) {
      unsigned int numSf = sIter - sBeg;
      if (distSol.first() > tol) {
        if (!currentDist.empty()) {
          oIter = currentDist.end();
          while (oIter != currentDist.begin() && distSol.first() < (*(oIter - 1)).second)
            --oIter;
          oIter = currentDist.insert(oIter, std::pair<unsigned int, double>(numSf, distSol.first()));
        } else {
          currentDist.emplace_back(numSf, distSol.first());
        }
      }
      if (distSol.numberOfSolutions() > 1 && distSol.second() > tol) {
        if (!currentDist.empty()) {
          oIter = currentDist.end();
          while (oIter != currentDist.begin() && distSol.second() < (*(oIter - 1)).second)
            --oIter;
          oIter = currentDist.insert(oIter, std::pair<unsigned int, double>(numSf, distSol.second()));
        } else {
          currentDist.emplace_back(numSf, distSol.second());
        }
      }
    }
  }
 
  // loop over surfaces, find valid intersections
  for (oIter = currentDist.begin(); oIter != currentDist.end(); ++oIter) {
    Amg::Vector3D xsct = position + propDir * direction * ((*oIter).second);
    if (targetSurfaces[(*oIter).first].first->isOnSurface(xsct, (*oIter).second, 0.001, 0.001)) {
      if (usePathLimit && path > 0. && path < ((*oIter).second)) {
        Amg::Vector3D endpoint = position + propDir * direction * path;
        return std::make_unique<Trk::CurvilinearParameters>(endpoint, parm.momentum(), parm.charge());
      }
      path = (*oIter).second;
      solutions.push_back((*oIter).first);
      const Trk::Surface* sf = targetSurfaces[(*oIter).first].first;
 
      if (returnCurv || sf->type() == Trk::SurfaceType::Cone) {
        return std::make_unique<Trk::CurvilinearParameters>(xsct, parm.momentum(), parm.charge());
      }
      return sf->createUniqueTrackParameters(xsct, parm.momentum(), parm.charge(), std::nullopt);
    }
  }
 
  return nullptr;
}
 
void
clearMaterialEffects(Trk::STEP_Propagator::Cache& cache)
{
  cache.m_delIoni = 0.;
  cache.m_delRad = 0.;
  cache.m_sigmaIoni = 0.;
  cache.m_sigmaRad = 0.;
}
 
// Calculate energy loss in MeV/mm.
double
dEds(Cache& cache, double p)
{
  cache.m_delIoni = 0.;
  cache.m_delRad = 0.;
  cache.m_kazL = 0.;
 
  if (cache.m_particle == Trk::geantino || cache.m_particle == Trk::nonInteractingMuon)
    return 0.;
  if (cache.m_material->x0() == 0 || cache.m_material->averageZ() == 0)
    return 0.;
 
  cache.m_delIoni =
    Trk::MaterialInteraction::dEdl_ionization(p, *(cache.m_material), cache.m_particle, cache.m_sigmaIoni, cache.m_kazL);
 
  cache.m_delRad = Trk::MaterialInteraction::dEdl_radiation(p, *(cache.m_material), cache.m_particle, cache.m_sigmaRad);
 
  double eLoss = cache.m_MPV ? 0.9 * cache.m_delIoni + 0.15 * cache.m_delRad : cache.m_delIoni + cache.m_delRad;
 
  return eLoss;
}
 
// dg/dlambda for non-electrons (g=dEdX and lambda=q/p).
 
double
dgdlambda(Cache& cache, double l)
{
  if (cache.m_particle == Trk::geantino || cache.m_particle == Trk::nonInteractingMuon)
    return 0.;
  if (cache.m_material->x0() == 0 || cache.m_material->averageZ() == 0)
    return 0.;
  if (cache.m_material->zOverAtimesRho() == 0)
    return 0.;
 
  double p = std::abs(1. / l);
  double m = Trk::ParticleMasses::mass[cache.m_particle];
  double me = Trk::ParticleMasses::mass[Trk::electron];
  double E = std::sqrt(p * p + m * m);
  double beta = p / E;
  double gamma = E / m;
  double I = 16.e-6 * std::pow(cache.m_material->averageZ(), 0.9);
  double kaz = 0.5 * 30.7075 * cache.m_material->zOverAtimesRho();
 
  // Bethe-Bloch
  double lnCore = 4. * me * me / (m * m * m * m * I * I * l * l * l * l) / (1. + 2. * gamma * me / m + me * me / m * m);
  double lnCore_deriv =
    -4. * me * me / (m * m * m * m * I * I) *
    std::pow(l * l * l * l + 2. * gamma * l * l * l * l * me / m + l * l * l * l * me * me / (m * m), -2) *
    (4. * l * l * l + 8. * me * l * l * l * gamma / m - 2. * me * l / (m * m * m * gamma) +
     4. * l * l * l * me * me / (m * m));
  double ln_deriv = 2. * l * m * m * std::log(lnCore) + lnCore_deriv / (lnCore * beta * beta);
  double Bethe_Bloch_deriv = -kaz * ln_deriv;
 
  // density effect, only valid for high energies (gamma > 10 -> p > 1GeV for muons)
  if (gamma > 10.) {
    double delta = 2. * std::log(28.816e-6 * std::sqrt(1000. * cache.m_material->zOverAtimesRho()) / I) +
                   2. * std::log(beta * gamma) - 1.;
    double delta_deriv = -2. / (l * beta * beta) + 2. * delta * l * m * m;
    Bethe_Bloch_deriv += kaz * delta_deriv;
  }
 
  // Bethe-Heitler
  double Bethe_Heitler_deriv = me * me / (m * m * cache.m_material->x0() * l * l * l * E);
 
  // Radiative corrections (e+e- pair production + photonuclear) for muons at energies above 8 GeV and below 1 TeV
  double radiative_deriv = 0.;
  if ((cache.m_particle == Trk::muon) && (E > 8000.)) {
    if (E < 1.e6) {
      radiative_deriv = 6.803e-5 / (cache.m_material->x0() * l * l * l * E) +
                        2. * 2.278e-11 / (cache.m_material->x0() * l * l * l) -
                        3. * 9.899e-18 * E / (cache.m_material->x0() * l * l * l);
    } else {
      radiative_deriv = 9.253e-5 / (cache.m_material->x0() * l * l * l * E);
    }
  }
 
  // return the total derivative
  if (cache.m_MPV) {
    return 0.9 * Bethe_Bloch_deriv + 0.15 * Bethe_Heitler_deriv + 0.15 * radiative_deriv; // Most probable value
  } else {
    return Bethe_Bloch_deriv + Bethe_Heitler_deriv + radiative_deriv; // Mean value
  }
}
 
// update material effects   // to follow change of material
void
updateMaterialEffects(Cache& cache, double mom, double sinTheta, double path)
{
  // collects material effects in between material dumps ( m_covariance )
 
  // collect straggling
  if (cache.m_straggling) {
    cache.m_covariance(4, 4) += cache.m_stragglingVariance;
    cache.m_stragglingVariance = 0.;
  }
 
  if (!cache.m_multipleScattering)
    return;
 
  double totalMomentumLoss = mom - cache.m_matupd_lastmom;
  double pathSinceLastUpdate = path - cache.m_matupd_lastpath;
 
  double pathAbs = std::abs(pathSinceLastUpdate);
 
  if (pathAbs < 1.e-03)
    return;
 
  double matX0 = cache.m_material->x0();
 
  // calculate number of layers : TODO : thickness to be adjusted
  int msLayers = int(pathAbs / cache.m_layXmax / matX0) + 1;
 
  double massSquared = Trk::ParticleMasses::mass[cache.m_particle] * Trk::ParticleMasses::mass[cache.m_particle];
  double layerThickness = pathAbs / msLayers;
  double radiationLengths = layerThickness / matX0;
  sinTheta = std::max(sinTheta, 1e-20); // avoid division by zero
  double remainingPath = pathAbs;
  double momentum = 0.;
  double mom2 = 0.;
  double E = 0.;
  double beta = 0.;
  double dLambdads = 0.;
  double thetaVariance = 0.;
 
  double average_dEds = totalMomentumLoss / pathAbs;
 
  double cumulatedVariance = cache.m_inputThetaVariance + cache.m_combinedCovariance(3, 3) + cache.m_covariance(3, 3);
  if (cumulatedVariance < 0) {
    cumulatedVariance = 0;
  }
  double cumulatedX0 = 0.;
 
  bool useCache = cache.m_extrapolationCache != nullptr;
  if (useCache) {
    double dX0 = std::abs(cache.m_combinedThickness) - pathAbs / matX0;
    if (dX0 < 0)
      dX0 = 0.;
    if (cache.m_extrapolationCache->x0tot() > 0)
      cumulatedX0 = cache.m_extrapolationCache->x0tot() + dX0;
  }
 
  // calculate multiple scattering by summing the contributions from the layers
  for (int layer = 1; layer <= msLayers; ++layer) {
 
    // calculate momentum in the middle of the layer by assuming a linear momentum loss
    momentum = cache.m_matupd_lastmom + totalMomentumLoss * (layer - 0.5) / msLayers;
 
    mom2 = momentum * momentum;
    E = std::sqrt(mom2 + massSquared);
    beta = momentum / E;
 
    double C0 = 13.6 * 13.6 / mom2 / beta / beta;
    double C1 = 2 * 0.038 * C0;
    double C2 = 0.038 * 0.038 * C0;
 
    double MS2 = radiationLengths;
 
    dLambdads = -cache.m_charge * average_dEds * E / (momentum * momentum * momentum);
    remainingPath -= layerThickness;
 
    // simple - step dependent formula
    // thetaVariance = C0*MS2 + C1*MS2*log(MS2) + C2*MS2*log(MS2)*log(MS2);
 
    // replaced by the step-size independent code below
    if (!useCache) {
      cumulatedX0 = cumulatedVariance / C0;
      if (cumulatedX0 > 0.001) {
        double lX0 = log(cumulatedX0);
        cumulatedX0 = cumulatedX0 / (1 + 2 * 0.038 * lX0 + 0.038 * 0.038 * lX0 * lX0);
      }
    }
 
    double MS2s = MS2 + cumulatedX0;
    thetaVariance = C0 * MS2 + C1 * MS2s * log(MS2s) + C2 * MS2s * log(MS2s) * log(MS2s);
 
    if (cumulatedX0 > 0.001) {
      double lX0 = log(cumulatedX0);
      thetaVariance += -C1 * cumulatedX0 * lX0 - C2 * cumulatedX0 * lX0 * lX0;
    }
 
    // Calculate ms covariance contributions and scale
    double varScale = cache.m_scatteringScale * cache.m_scatteringScale;
    double positionVariance = thetaVariance * (layerThickness * layerThickness / 3. + remainingPath * layerThickness +
                                               remainingPath * remainingPath);
    cache.m_covariance(0, 0) += varScale * positionVariance;
    cache.m_covariance(1, 1) += varScale * positionVariance;
    cache.m_covariance.fillSymmetric(
      2, 0, cache.m_covariance(2, 0) + varScale * thetaVariance / (sinTheta) * (layerThickness / 2. + remainingPath));
    cache.m_covariance(2, 2) += varScale * thetaVariance / (sinTheta * sinTheta);
    cache.m_covariance.fillSymmetric(
      3, 1, cache.m_covariance(3, 1) + varScale * thetaVariance * (-layerThickness / 2. - remainingPath));
    cache.m_covariance(3, 3) += varScale * thetaVariance;
    cache.m_covariance(4, 4) +=
      varScale * 3. * thetaVariance * thetaVariance * layerThickness * layerThickness * dLambdads * dLambdads;
    cumulatedVariance += varScale * thetaVariance;
    cumulatedX0 += MS2;
  }
 
  cache.m_matupd_lastmom = mom;
  cache.m_matupd_lastpath = path;
}
 
// Multiple scattering and straggling contribution to the covariance matrix
 
void
covarianceContribution(Cache& cache,
                       const Trk::TrackParameters* trackParameters,
                       double path,
                       const Trk::TrackParameters* targetParms,
                       AmgSymMatrix(5)& measurementCovariance)
{
  // kinematics
  double finalMomentum = targetParms->momentum().mag();
 
  // first update to make sure all material counted
  updateMaterialEffects(cache, finalMomentum, sin(trackParameters->momentum().theta()), path);
 
  double Jac[21];
  Trk::RungeKuttaUtils::jacobianTransformCurvilinearToLocal(*targetParms, Jac);
 
  // Transform multiple scattering and straggling covariance from curvilinear to local system
  AmgSymMatrix(5) localMSCov =
    Trk::RungeKuttaUtils::newCovarianceMatrix(Jac, cache.m_combinedCovariance + cache.m_covariance);
 
  measurementCovariance += localMSCov;
}
 
// Multiple scattering and straggling contribution to the covariance matrix in curvilinear representation
 
void
covarianceContribution(Cache& cache,
                       const Trk::TrackParameters* trackParameters,
                       double path,
                       double finalMomentum,
                       AmgSymMatrix(5)& measurementCovariance)
{
  // first update to make sure all material counted
  updateMaterialEffects(cache, finalMomentum, sin(trackParameters->momentum().theta()), path);
 
  // Add measurement errors and multiple scattering + straggling covariance
  measurementCovariance += cache.m_combinedCovariance + cache.m_covariance;
}
 
// Runge Kutta trajectory model (units->mm,MeV,kGauss)
//
// Runge Kutta method is adaptive Runge-Kutta-Nystrom.
// This is the default STEP method
 
// We compile this package with optimization, even in debug builds; otherwise,
// the heavy use of Eigen makes it too slow.  However, from here we may call
// to out-of-line Eigen code that is linked from other DSOs; in that case,
// it would not be optimized.  Avoid this by forcing all Eigen code
// to be inlined here if possible.
ATH_FLATTEN
bool
rungeKuttaStep(Cache& cache,
               bool errorPropagation,
               double& h,
               double* ATH_RESTRICT  P,
               double* ATH_RESTRICT dDir,
               double* ATH_RESTRICT BG1,
               bool& firstStep,
               double& distanceStepped)
{
  constexpr double sol = 0.0299792458; //speed of light * kilogauss in method units
  double charge = 0;
  P[6] >= 0. ? charge = 1. : charge = -1.; // Set charge
  double lambda1 = P[6];
  double lambda2 = P[6]; // Store inverse momentum for Jacobian transport
  double lambda3 = P[6];
  double lambda4 = P[6];
  double dP1 = 0.;
  double dP2 = 0.;
  double dP3 = 0.;
  double dP4 = 0.; // dp/ds = -g*E/p for positive g=dE/ds
  double dL1 = 0.;
  double dL2 = 0.;
  double dL3 = 0.;
  double dL4 = 0.;                              // factor used for calculating dCM/dCM, P[41], in the Jacobian.
  double initialMomentum = std::abs(1. / P[6]); // Set initial momentum
  const Amg::Vector3D initialPos(P[0], P[1], P[2]);   // Set initial values for position
  const Amg::Vector3D initialDir(P[3], P[4], P[5]);   // Set initial values for direction.
  if (!Amg::saneVector(initialPos) || !Amg::saneVector(initialDir)) return false;
  // Directions at the different points. Used by the error propagation
  Amg::Vector3D dir1;
  Amg::Vector3D dir2;
  Amg::Vector3D dir3;
  Amg::Vector3D dir4;
  // Bx, By, Bz, dBx/dx, dBx/dy, dBx/dz, dBy/dx, dBy/dy, dBy/dz, dBz/dx, dBz/dy,dBz/dz
  double BG23[12] = { 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0. };
  // The gradients are used by the error propagation
  double BG4[12] = { 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0. };
  double g = 0.;                                                 // Energyloss in Mev/mm.
  double dgdl = 0.;                                              // dg/dlambda in Mev/mm.
  double particleMass = Trk::ParticleMasses::mass[cache.m_particle]; // Get particle mass from ParticleHypothesis
  int steps = 0;
 
  // POINT 1. Only calculate this once per step, even if step is rejected. This
  // point is independant of the step length, h
  double momentum = initialMomentum; // Current momentum
  if (cache.m_energyLoss && cache.m_matPropOK) {
    g = dEds(cache, momentum); // Use the same energy loss throughout the step.
    double E = std::sqrt(momentum * momentum + particleMass * particleMass);
    dP1 = g * E / momentum;
    if (errorPropagation) {
      if (cache.m_includeGgradient) {
        dgdl = dgdlambda(cache, lambda1); // Use this value throughout the step.
      }
      dL1 =
        -lambda1 * lambda1 * g * E * (3. - (momentum * momentum) / (E * E)) - lambda1 * lambda1 * lambda1 * E * dgdl;
    }
  }
 
  Amg::Vector3D pos = initialPos; // Coordinate solution
  Amg::Vector3D dir = initialDir; // Direction solution
  dir1 = dir;
  if (firstStep) { // Poll BG1 if this is the first step, else use recycled BG4
    firstStep = false;
    // Get the gradients needed for the error propagation if errorPropagation=true
    getMagneticField(cache,
                     pos,
                     errorPropagation,
                     BG1); // Get the gradients needed for the error propagation if errorPropagation=true
  }
  // Lorentz force, d2r/ds2 = lambda * (dir x B)
  Amg::Vector3D k1(
    dir.y() * BG1[2] - dir.z() * BG1[1], dir.z() * BG1[0] - dir.x() * BG1[2], dir.x() * BG1[1] - dir.y() * BG1[0]);
  k1 = sol * lambda1 * k1;
 
  while (true) { // Repeat step until error estimate is within the requested tolerance
    if (steps++ > cache.m_maxSteps)
      return false; // Abort propagation
    // POINT 2
    if (cache.m_energyLoss && cache.m_matPropOK) {
      momentum = initialMomentum + (h / 2.) * dP1;
      if (momentum <= cache.m_momentumCutOff)
        return false; // Abort propagation
      double E = std::sqrt(momentum * momentum + particleMass * particleMass);
      dP2 = g * E / momentum;
      lambda2 = charge / momentum;
      if (errorPropagation) {
        dL2 =
          -lambda2 * lambda2 * g * E * (3. - (momentum * momentum) / (E * E)) - lambda2 * lambda2 * lambda2 * E * dgdl;
      }
    }
    pos = initialPos + (h / 2.) * initialDir + (h * h / 8.) * k1;
    dir = initialDir + (h / 2.) * k1;
    dir2 = dir;
 
    getMagneticField(cache, pos, errorPropagation, BG23);
    Amg::Vector3D k2(dir.y() * BG23[2] - dir.z() * BG23[1],
                     dir.z() * BG23[0] - dir.x() * BG23[2],
                     dir.x() * BG23[1] - dir.y() * BG23[0]);
    k2 = sol * lambda2 * k2;
 
    // POINT 3. Same position and B-field as point 2.
    if (cache.m_energyLoss && cache.m_matPropOK) {
      momentum = initialMomentum + (h / 2.) * dP2;
      if (momentum <= cache.m_momentumCutOff)
        return false; // Abort propagation
      double E = std::sqrt(momentum * momentum + particleMass * particleMass);
      dP3 = g * E / momentum;
      lambda3 = charge / momentum;
      if (errorPropagation) {
        dL3 =
          -lambda3 * lambda3 * g * E * (3. - (momentum * momentum) / (E * E)) - lambda3 * lambda3 * lambda3 * E * dgdl;
      }
    }
    dir = initialDir + (h / 2.) * k2;
    dir3 = dir;
    Amg::Vector3D k3(dir.y() * BG23[2] - dir.z() * BG23[1],
                     dir.z() * BG23[0] - dir.x() * BG23[2],
                     dir.x() * BG23[1] - dir.y() * BG23[0]);
    k3 = sol * lambda3 * k3;
 
    // POINT 4
    if (cache.m_energyLoss && cache.m_matPropOK) {
      momentum = initialMomentum + h * dP3;
      if (momentum <= cache.m_momentumCutOff)
        return false; // Abort propagation
      double E = std::sqrt(momentum * momentum + particleMass * particleMass);
      dP4 = g * E / momentum;
      lambda4 = charge / momentum;
      if (errorPropagation) {
        dL4 =
          -lambda4 * lambda4 * g * E * (3. - (momentum * momentum) / (E * E)) - lambda4 * lambda4 * lambda4 * E * dgdl;
      }
    }
    pos = initialPos + h * initialDir + (h * h / 2.) * k3;
    dir = initialDir + h * k3;
    dir4 = dir;
 
    // MT Field cache is stored in cache
    getMagneticField(cache, pos, errorPropagation, BG4);
    Amg::Vector3D k4(
      dir.y() * BG4[2] - dir.z() * BG4[1], dir.z() * BG4[0] - dir.x() * BG4[2], dir.x() * BG4[1] - dir.y() * BG4[0]);
    k4 = sol * lambda4 * k4;
 
    // Estimate local error and avoid division by zero
    Amg::Vector3D errorPos((h * h) * (k1 - k2 - k3 + k4));
    double errorEstimate = std::max(errorPos.mag(), 1e-20);
 
    // Use the error estimate to calculate new step length. h is returned by reference.
    distanceStepped = h; // Store old step length.
    h = h * std::min(std::max(0.25, std::sqrt(std::sqrt(cache.m_tolerance / errorEstimate))), 4.);
 
    // Repeat step with the new step size if error is too big.
    if (errorEstimate > 4. * cache.m_tolerance)
      continue;
 
    // Step was ok. Store solutions.
    // Update positions.
    pos = initialPos + distanceStepped * initialDir + (distanceStepped * distanceStepped / 6.) * (k1 + k2 + k3);
    P[0] = pos.x();
    P[1] = pos.y();
    P[2] = pos.z();
 
    // update directions
    dir = initialDir + (distanceStepped / 6.) * (k1 + 2. * k2 + 2. * k3 + k4);
    P[3] = dir.x();
    P[4] = dir.y();
    P[5] = dir.z();
 
    // Normalize direction
    double norm = 1. / std::sqrt(P[3] * P[3] + P[4] * P[4] + P[5] * P[5]);
    P[3] = norm * P[3];
    P[4] = norm * P[4];
    P[5] = norm * P[5];
 
    // Update inverse momentum if energyloss is switched on
    if (cache.m_energyLoss && cache.m_matPropOK) {
      momentum = initialMomentum + (distanceStepped / 6.) * (dP1 + 2. * dP2 + 2. * dP3 + dP4);
      if (momentum <= cache.m_momentumCutOff)
        return false; // Abort propagation
      P[6] = charge / momentum;
    }
 
    // dDir provides a small correction to the final tiny step in PropagateWithJacobian
    dDir[0] = k4.x();
    dDir[1] = k4.y();
    dDir[2] = k4.z();
 
    // Transport Jacobian using the same step length, points and magnetic fields as for the track parameters
    // BG contains Bx, By, Bz, dBx/dx, dBx/dy, dBx/dz, dBy/dx, dBy/dy, dBy/dz, dBz/dx, dBz/dy, dBz/dz
    //                0   1   2   3       4       5       6       7       8       9       10      11
    if (errorPropagation) {
      double initialjLambda = P[41]; // dLambda/dLambda
      double jLambda = initialjLambda;
      double jdL1 = 0.;
      double jdL2 = 0.;
      double jdL3 = 0.;
      double jdL4 = 0.;
 
      for (int i = 7; i < 42; i += 7) {
 
        // POINT 1
        const Amg::Vector3D initialjPos(P[i], P[i + 1], P[i + 2]);
        const Amg::Vector3D initialjDir(P[i + 3], P[i + 4], P[i + 5]);
 
        if (!Amg::saneVector(initialjPos) || !Amg::saneVector(initialjDir)) return false;
 
        Amg::Vector3D jPos = initialjPos;
        Amg::Vector3D jDir = initialjDir;
 
        // B-field terms
        Amg::Vector3D jk1(jDir.y() * BG1[2] - jDir.z() * BG1[1],
                          jDir.z() * BG1[0] - jDir.x() * BG1[2],
                          jDir.x() * BG1[1] - jDir.y() * BG1[0]);
 
        // B-field gradient terms
        if (cache.m_includeBgradients) {
          Amg::Vector3D C(
            (dir1.y() * BG1[9] - dir1.z() * BG1[6]) * jPos.x() + (dir1.y() * BG1[10] - dir1.z() * BG1[7]) * jPos.y() +
              (dir1.y() * BG1[11] - dir1.z() * BG1[8]) * jPos.z(),
            (dir1.z() * BG1[3] - dir1.x() * BG1[9]) * jPos.x() + (dir1.z() * BG1[4] - dir1.x() * BG1[10]) * jPos.y() +
              (dir1.z() * BG1[5] - dir1.x() * BG1[11]) * jPos.z(),
            (dir1.x() * BG1[6] - dir1.y() * BG1[3]) * jPos.x() + (dir1.x() * BG1[7] - dir1.y() * BG1[4]) * jPos.y() +
              (dir1.x() * BG1[8] - dir1.y() * BG1[5]) * jPos.z());
          jk1 = jk1 + C;
        }
        jk1 = sol * lambda1 * jk1;
 
        // Last column of the A-matrix
        if (i == 35) {          // Only dLambda/dLambda, in the last row of the jacobian, is different from zero
          jdL1 = dL1 * jLambda; // Energy loss term. dL1 = 0 if no material effects -> jLambda = P[41] is unchanged
          jk1 = jk1 + k1 * jLambda / lambda1; // B-field terms
        }
 
        // POINT 2
        jPos = initialjPos + (distanceStepped / 2.) * initialjDir + (distanceStepped * distanceStepped / 8.) * jk1;
        jDir = initialjDir + (distanceStepped / 2.) * jk1;
 
        Amg::Vector3D jk2(jDir.y() * BG23[2] - jDir.z() * BG23[1],
                          jDir.z() * BG23[0] - jDir.x() * BG23[2],
                          jDir.x() * BG23[1] - jDir.y() * BG23[0]);
 
        if (cache.m_includeBgradients) {
          Amg::Vector3D C((dir2.y() * BG23[9] - dir2.z() * BG23[6]) * jPos.x() +
                            (dir2.y() * BG23[10] - dir2.z() * BG23[7]) * jPos.y() +
                            (dir2.y() * BG23[11] - dir2.z() * BG23[8]) * jPos.z(),
                          (dir2.z() * BG23[3] - dir2.x() * BG23[9]) * jPos.x() +
                            (dir2.z() * BG23[4] - dir2.x() * BG23[10]) * jPos.y() +
                            (dir2.z() * BG23[5] - dir2.x() * BG23[11]) * jPos.z(),
                          (dir2.x() * BG23[6] - dir2.y() * BG23[3]) * jPos.x() +
                            (dir2.x() * BG23[7] - dir2.y() * BG23[4]) * jPos.y() +
                            (dir2.x() * BG23[8] - dir2.y() * BG23[5]) * jPos.z());
          jk2 = jk2 + C;
        }
        jk2 = sol * lambda2 * jk2;
 
        if (i == 35) {
          jLambda = initialjLambda + (distanceStepped / 2.) * jdL1;
          jdL2 = dL2 * jLambda;
          jk2 = jk2 + k2 * jLambda / lambda2;
        }
 
        // POINT 3
        jDir = initialjDir + (distanceStepped / 2.) * jk2;
 
        Amg::Vector3D jk3(jDir.y() * BG23[2] - jDir.z() * BG23[1],
                          jDir.z() * BG23[0] - jDir.x() * BG23[2],
                          jDir.x() * BG23[1] - jDir.y() * BG23[0]);
 
        if (cache.m_includeBgradients) {
          Amg::Vector3D C((dir3.y() * BG23[9] - dir3.z() * BG23[6]) * jPos.x() +
                            (dir3.y() * BG23[10] - dir3.z() * BG23[7]) * jPos.y() +
                            (dir3.y() * BG23[11] - dir3.z() * BG23[8]) * jPos.z(),
                          (dir3.z() * BG23[3] - dir3.x() * BG23[9]) * jPos.x() +
                            (dir3.z() * BG23[4] - dir3.x() * BG23[10]) * jPos.y() +
                            (dir3.z() * BG23[5] - dir3.x() * BG23[11]) * jPos.z(),
                          (dir3.x() * BG23[6] - dir3.y() * BG23[3]) * jPos.x() +
                            (dir3.x() * BG23[7] - dir3.y() * BG23[4]) * jPos.y() +
                            (dir3.x() * BG23[8] - dir3.y() * BG23[5]) * jPos.z());
          jk3 = jk3 + C;
        }
        jk3 = sol * lambda3 * jk3;
 
        if (i == 35) {
          jLambda = initialjLambda + (distanceStepped / 2.) * jdL2;
          jdL3 = dL3 * jLambda;
          jk3 = jk3 + k3 * jLambda / lambda3;
        }
 
        // POINT 4
        jPos = initialjPos + distanceStepped * initialjDir + (distanceStepped * distanceStepped / 2.) * jk3;
        jDir = initialjDir + distanceStepped * jk3;
 
        Amg::Vector3D jk4(jDir.y() * BG4[2] - jDir.z() * BG4[1],
                          jDir.z() * BG4[0] - jDir.x() * BG4[2],
                          jDir.x() * BG4[1] - jDir.y() * BG4[0]);
 
        if (cache.m_includeBgradients) {
          Amg::Vector3D C(
            (dir4.y() * BG4[9] - dir4.z() * BG4[6]) * jPos.x() + (dir4.y() * BG4[10] - dir4.z() * BG4[7]) * jPos.y() +
              (dir4.y() * BG4[11] - dir4.z() * BG4[8]) * jPos.z(),
            (dir4.z() * BG4[3] - dir4.x() * BG4[9]) * jPos.x() + (dir4.z() * BG4[4] - dir4.x() * BG4[10]) * jPos.y() +
              (dir4.z() * BG4[5] - dir4.x() * BG4[11]) * jPos.z(),
            (dir4.x() * BG4[6] - dir4.y() * BG4[3]) * jPos.x() + (dir4.x() * BG4[7] - dir4.y() * BG4[4]) * jPos.y() +
              (dir4.x() * BG4[8] - dir4.y() * BG4[5]) * jPos.z());
          jk4 = jk4 + C;
        }
        jk4 = sol * lambda4 * jk4;
 
        if (i == 35) {
          jLambda = initialjLambda + distanceStepped * jdL3;
          jdL4 = dL4 * jLambda;
          jk4 = jk4 + k4 * jLambda / lambda4;
        }
 
        // solution
        jPos =
          initialjPos + distanceStepped * initialjDir + (distanceStepped * distanceStepped / 6.) * (jk1 + jk2 + jk3);
        jDir = initialjDir + (distanceStepped / 6.) * (jk1 + 2. * jk2 + 2. * jk3 + jk4);
        if (i == 35) {
          jLambda = initialjLambda + (distanceStepped / 6.) * (jdL1 + 2. * jdL2 + 2. * jdL3 + jdL4);
        }
 
        // Update positions
        P[i] = jPos.x();
        P[i + 1] = jPos.y();
        P[i + 2] = jPos.z();
 
        // update directions
        P[i + 3] = jDir.x();
        P[i + 4] = jDir.y();
        P[i + 5] = jDir.z();
      }
      P[41] = jLambda; // update dLambda/dLambda
    }
 
    // Store BG4 for use as BG1 in the next step
    for (int i = 0; i < 12; ++i) {
      BG1[i] = BG4[i];
    }
    return true;
  }
}
// Runge Kutta main program for propagation with or without Jacobian
bool
propagateWithJacobianImpl(Cache& cache,
                          bool errorPropagation,
                          Trk::SurfaceType surfaceType,
                          double* ATH_RESTRICT targetSurface,
                          double* ATH_RESTRICT P,
                          double& path)
{
  double maxPath = cache.m_maxPath;      // Max path allowed
  double* pos = &P[0];             // Start coordinates
  double* dir = &P[3];             // Start directions
  double dDir[3] = { 0., 0., 0. }; // Start directions derivs. Zero in case of no RK steps
  int targetPassed = 0;            // how many times have we passed the target?
  double previousDistance = 0.;
  double distanceStepped = 0.;
  bool distanceEstimationSuccessful = false;                           // Was the distance estimation successful?
  double BG1[12] = { 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0. }; // Bx, By, Bz, dBx/dx, dBx/dy, dBx/dz,
  // dBy/dx, dBy/dy, dBy/dz, dBz/dx, dBz/dy, dBz/dz at first point
  bool firstStep = true;    // Poll BG1, else recycle BG4
  double absolutePath = 0.; // Absolute path to register oscillating behaviour
  int steps = 0;
  path = 0.; // signed path of the trajectory
  double mom = 0.;
  double beta = 1.;
 
  double distanceToTarget = Trk::RungeKuttaUtils::stepEstimator(
      surfaceType, targetSurface, P, distanceEstimationSuccessful);
  if (!distanceEstimationSuccessful) {
    return false;
  }
 
  // Set initial step length to 100mm or the distance to the target surface.
  double h = 0;
  distanceToTarget > 100. ? h = 100. : distanceToTarget < -100. ? h = -100. : h = distanceToTarget;
 
  // Step to within distanceTolerance, then do the rest as a Taylor expansion.
  // Keep distanceTolerance within [1 nanometer, 10 microns].
  // This means that no final Taylor expansions beyond 10 microns and no
  // Runge-Kutta steps less than 1 nanometer are allowed.
  double distanceTolerance = std::min(std::max(std::abs(distanceToTarget) * cache.m_tolerance, 1e-6), 1e-2);
 
  while (std::abs(distanceToTarget) > distanceTolerance) { // Step until within tolerance
    // Do the step. Stop the propagation if the energy goes below m_momentumCutOff
    if (!rungeKuttaStep(cache, errorPropagation, h, P, dDir, BG1, firstStep, distanceStepped))
      return false;
    path += distanceStepped;
    absolutePath += std::abs(distanceStepped);
 
    if (std::abs(distanceStepped) > 0.001) {
      cache.m_sigmaIoni = cache.m_sigmaIoni - cache.m_kazL * log(std::abs(distanceStepped)); // the non-linear term
    }
    // update straggling covariance
    if (errorPropagation && cache.m_straggling) {
      double sigTot2 = cache.m_sigmaIoni * cache.m_sigmaIoni + cache.m_sigmaRad * cache.m_sigmaRad;
      // /(beta*beta*p*p*p*p) transforms Var(E) to Var(q/p)
      mom = std::abs(1. / P[6]);
      beta = mom / std::sqrt(mom * mom + cache.m_particleMass * cache.m_particleMass);
      double bp2 = beta * mom * mom;
      cache.m_stragglingVariance += sigTot2 / (bp2 * bp2) * distanceStepped * distanceStepped;
    }
    if (cache.m_matstates || errorPropagation)
      cache.m_combinedEloss.update(cache.m_delIoni * distanceStepped,
                                   cache.m_sigmaIoni * std::abs(distanceStepped),
                                   cache.m_delRad * distanceStepped,
                                   cache.m_sigmaRad * std::abs(distanceStepped),
                                   cache.m_MPV);
    // Calculate new distance to target
    previousDistance = std::abs(distanceToTarget);
    distanceToTarget = Trk::RungeKuttaUtils::stepEstimator(
        surfaceType, targetSurface, P, distanceEstimationSuccessful);
    if (!distanceEstimationSuccessful)
      return false;
 
    // If h and distance are in opposite directions, target is passed. Flip propagation direction
    if (h * distanceToTarget < 0.) {
      h = -h; // Flip direction
      ++targetPassed;
    }
    // don't step beyond surface
    if (std::abs(h) > std::abs(distanceToTarget))
      h = distanceToTarget;
 
    // Abort if maxPath is reached or solution is diverging
    if ((targetPassed > 3 && std::abs(distanceToTarget) >= previousDistance) || (absolutePath > maxPath))
      return false;
 
    if (steps++ > cache.m_maxSteps)
      return false; // Too many steps, something is wrong
  }
 
  if (cache.m_material && cache.m_material->x0() != 0.)
    cache.m_combinedThickness += std::abs(path) / cache.m_material->x0();
 
  // Use Taylor expansions to step the remaining distance (typically microns).
  path = path + distanceToTarget;
 
  // pos = pos + h*dir + 1/2*h*h*dDir. Second order Taylor expansion.
  pos[0] = pos[0] + distanceToTarget * (dir[0] + 0.5 * distanceToTarget * dDir[0]);
  pos[1] = pos[1] + distanceToTarget * (dir[1] + 0.5 * distanceToTarget * dDir[1]);
  pos[2] = pos[2] + distanceToTarget * (dir[2] + 0.5 * distanceToTarget * dDir[2]);
 
  // dir = dir + h*dDir. First order Taylor expansion (Euler).
  dir[0] = dir[0] + distanceToTarget * dDir[0];
  dir[1] = dir[1] + distanceToTarget * dDir[1];
  dir[2] = dir[2] + distanceToTarget * dDir[2];
 
  // Normalize dir
  double norm = 1. / std::sqrt(dir[0] * dir[0] + dir[1] * dir[1] + dir[2] * dir[2]);
  dir[0] = norm * dir[0];
  dir[1] = norm * dir[1];
  dir[2] = norm * dir[2];
  P[42] = dDir[0];
  P[43] = dDir[1];
  P[44] = dDir[2];
  return true;
}
 
// Main function for track propagation with or without jacobian
std::unique_ptr<Trk::TrackParameters>
propagateRungeKuttaImpl(Cache& cache,
                        bool errorPropagation,
                        const Trk::TrackParameters& inputTrackParameters,
                        const Trk::Surface& targetSurface,
                        Trk::PropDirection propagationDirection,
                        const Trk::MagneticFieldProperties& mft,
                        Trk::ParticleHypothesis particle,
                        const Trk::BoundaryCheck& boundaryCheck,
                        double* Jacobian,
                        bool returnCurv)
{
  // Store for later use
  cache.m_particle = particle;
  cache.m_charge = inputTrackParameters.charge();
 
  std::unique_ptr<Trk::TrackParameters> trackParameters{};
 
  // Bfield mode
  mft.magneticFieldMode() == Trk::FastField ? cache.m_solenoid = true : cache.m_solenoid = false;
 
  // Check inputvalues
  if (cache.m_tolerance <= 0.)
    return nullptr;
  if (cache.m_momentumCutOff < 0.)
    return nullptr;
 
  // Set momentum to 1e10 (straight line) and charge to + if q/p is zero
  if (inputTrackParameters.parameters()[Trk::qOverP] == 0) {
    trackParameters = createStraightLine(&inputTrackParameters);
    if (!trackParameters) {
      return nullptr;
    }
  } else {
    trackParameters.reset(inputTrackParameters.clone());
  }
 
  if (std::abs(1. / trackParameters->parameters()[Trk::qOverP]) <= cache.m_momentumCutOff) {
    return nullptr;
  }
 
  // Check for empty volumes. If x != x then x is not a number.
  if (cache.m_matPropOK && ((cache.m_material->zOverAtimesRho() == 0.) || (cache.m_material->x0() == 0.) ||
                            (cache.m_material->zOverAtimesRho() != cache.m_material->zOverAtimesRho()))) {
    cache.m_matPropOK = false;
  }
  if (cache.m_matPropOK && cache.m_straggling)
    cache.m_stragglingVariance = 0.;
  if (errorPropagation || cache.m_matstates) {
    cache.m_combinedCovariance.setZero();
    cache.m_covariance.setZero();
    // this needs debugging
    cache.m_inputThetaVariance = trackParameters->covariance() ? (*trackParameters->covariance())(3, 3) : 0.;
    cache.m_combinedEloss.set(0., 0., 0., 0., 0., 0.);
    cache.m_combinedThickness = 0.;
  }
 
  if (!Trk::RungeKuttaUtils::transformLocalToGlobal(errorPropagation, *trackParameters, cache.m_P)) {
    return nullptr;
  }
  double path = 0.;
 
  const Amg::Transform3D& T = targetSurface.transform();
  Trk::SurfaceType ty = targetSurface.type();
 
  if (ty == Trk::SurfaceType::Plane || ty == Trk::SurfaceType::Disc) {
    double s[4];
    double d = T(0, 3) * T(0, 2) + T(1, 3) * T(1, 2) + T(2, 3) * T(2, 2);
 
    if (d >= 0.) {
      s[0] = T(0, 2);
      s[1] = T(1, 2);
      s[2] = T(2, 2);
      s[3] = d;
    } else {
      s[0] = -T(0, 2);
      s[1] = -T(1, 2);
      s[2] = -T(2, 2);
      s[3] = -d;
    }
    if (!propagateWithJacobianImpl(cache, errorPropagation, ty, s, cache.m_P, path)) {
      return nullptr;
    }
  }
 
  else if (ty == Trk::SurfaceType::Line) {
 
    double s[6] = { T(0, 3), T(1, 3), T(2, 3), T(0, 2), T(1, 2), T(2, 2) };
    if (!propagateWithJacobianImpl(cache, errorPropagation, ty, s, cache.m_P, path)) {
      return nullptr;
    }
  }
 
  else if (ty == Trk::SurfaceType::Cylinder) {
 
    const Trk::CylinderSurface* cyl = static_cast<const Trk::CylinderSurface*>(&targetSurface);
    double s[9] = { T(0, 3), T(1, 3), T(2, 3),           T(0, 2),
                    T(1, 2), T(2, 2), cyl->bounds().r(), (double)propagationDirection,
                    0. };
    if (!propagateWithJacobianImpl(cache, errorPropagation, ty, s, cache.m_P, path)) {
      return nullptr;
    }
  }
 
  else if (ty == Trk::SurfaceType::Cone) {
 
    double k = static_cast<const Trk::ConeSurface*>(&targetSurface)->bounds().tanAlpha();
    k = k * k + 1.;
    double s[9] = { T(0, 3), T(1, 3), T(2, 3), T(0, 2), T(1, 2), T(2, 2), k, (double)propagationDirection, 0. };
    if (!propagateWithJacobianImpl(cache, errorPropagation, ty, s, cache.m_P, path)) {
      return nullptr;
    }
  }
 
  else if (ty == Trk::SurfaceType::Perigee) {
 
    double s[6] = { T(0, 3), T(1, 3), T(2, 3), 0., 0., 1. };
    if (!propagateWithJacobianImpl(cache, errorPropagation, ty, s, cache.m_P, path)) {
      return nullptr;
    }
  }
 
  else { // assume curvilinear
 
    double s[4];
    double d = T(0, 3) * T(0, 2) + T(1, 3) * T(1, 2) + T(2, 3) * T(2, 2);
 
    if (d >= 0.) {
      s[0] = T(0, 2);
      s[1] = T(1, 2);
      s[2] = T(2, 2);
      s[3] = d;
    } else {
      s[0] = -T(0, 2);
      s[1] = -T(1, 2);
      s[2] = -T(2, 2);
      s[3] = -d;
    }
    if (!propagateWithJacobianImpl(cache, errorPropagation, ty, s, cache.m_P, path)) {
      return nullptr;
    }
  }
 
  if (propagationDirection * path < 0.) {
    return nullptr;
  }
 
  double localp[5];
  // output in curvilinear parameters
  if (returnCurv || ty == Trk::SurfaceType::Cone) {
 
    Trk::RungeKuttaUtils::transformGlobalToLocal(cache.m_P, localp);
    Amg::Vector3D gp(cache.m_P[0], cache.m_P[1], cache.m_P[2]);
 
    if (boundaryCheck && !targetSurface.isOnSurface(gp)) {
      return nullptr;
    }
 
    if (!errorPropagation || !trackParameters->covariance()) {
      return std::make_unique<Trk::CurvilinearParameters>(gp, localp[2], localp[3], localp[4]);
    }
 
    double useless[2];
    Trk::RungeKuttaUtils::transformGlobalToCurvilinear(true, cache.m_P, useless, Jacobian);
    AmgSymMatrix(5) measurementCovariance =
      Trk::RungeKuttaUtils::newCovarianceMatrix(Jacobian, *trackParameters->covariance());
 
    if (cache.m_matPropOK && (cache.m_multipleScattering || cache.m_straggling) && std::abs(path) > 0.)
      covarianceContribution(cache, trackParameters.get(), path, std::abs(1. / cache.m_P[6]), measurementCovariance);
 
    return std::make_unique<Trk::CurvilinearParameters>(
      gp, localp[2], localp[3], localp[4], std::move(measurementCovariance));
  }
 
  // Common transformation for all surfaces
  Trk::RungeKuttaUtils::transformGlobalToLocal(&targetSurface, errorPropagation, cache.m_P, localp, Jacobian);
 
  if (boundaryCheck) {
    Amg::Vector2D localPosition(localp[0], localp[1]);
    if (!targetSurface.insideBounds(localPosition, 0.)) {
      return nullptr;
    }
  }
 
  auto onTargetSurf =
    targetSurface.createUniqueTrackParameters(localp[0], localp[1], localp[2], localp[3], localp[4], std::nullopt);
 
  if (!errorPropagation || !trackParameters->covariance()) {
    return onTargetSurf;
  }
 
  // Errormatrix is included. Use Jacobian to calculate new covariance
  AmgSymMatrix(5) measurementCovariance =
    Trk::RungeKuttaUtils::newCovarianceMatrix(Jacobian, *trackParameters->covariance());
 
  // Calculate multiple scattering and straggling covariance contribution.
  if (cache.m_matPropOK && (cache.m_multipleScattering || cache.m_straggling) && std::abs(path) > 0.)
    covarianceContribution(cache, trackParameters.get(), path, onTargetSurf.get(), measurementCovariance);
 
  return targetSurface.createUniqueTrackParameters(
    localp[0], localp[1], localp[2], localp[3], localp[4], std::move(measurementCovariance));
}
 
} // end of anonymous namespace
 
// Constructor
 
Trk::STEP_Propagator::STEP_Propagator(const std::string& p, const std::string& n, const IInterface* t)
    : AthAlgTool(p, n, t),
      m_tolerance(1e-5)  // Error tolerance of the propagator. A low tolerance gives a high accuracy.
      ,m_materialEffects(true)  // Switches off all material effects if false. Does nothing when true.
      ,m_includeBgradients(true)  // Include B-field gradients into the error propagation?
      ,m_includeGgradient(false)  // Include dg/dlambda into the error propagation? Only relevant when energy loss is true.
      ,m_momentumCutOff(50.)  // Minimum allowed momentum in MeV.
      ,m_multipleScattering(true)  // Add multiple scattering to the covariance matrix?
      ,m_energyLoss(true)  // Include energy loss?
      ,m_detailedEloss(true)  // Provide the extended EnergyLoss object with MopIonization etc.
      ,m_straggling(true)  // Add energy loss fluctuations (straggling) to the covariance matrix?
      ,m_MPV(false)  // Use the most probable value of the energy loss, else use the mean energy loss.
      ,m_stragglingScale(1.)  // Scale for adjusting the width of the energy loss fluctuations.
      ,m_scatteringScale(1.)  // Scale for adjusting the multiple scattering contribution to the covariance matrix.
      ,m_maxPath(100000.)  // Maximum propagation length in mm.
      ,m_maxSteps(10000)  // Maximum number of allowed steps (to avoid infinite loops).
      ,m_layXmax(1.)  // maximal layer thickness for multiple scattering calculations
      ,m_simulation(false)  // flag for simulation mode
      ,m_rndGenSvc("AthRNGSvc", n)
      ,m_randomEngineName("FatrasRnd") {
  declareInterface<Trk::IPropagator>(this);
  declareProperty("Tolerance", m_tolerance);
  declareProperty("MaterialEffects", m_materialEffects);
  declareProperty("IncludeBgradients", m_includeBgradients);
  declareProperty("IncludeGgradient", m_includeGgradient);
  declareProperty("MomentumCutOff", m_momentumCutOff);
  declareProperty("MultipleScattering", m_multipleScattering);
  declareProperty("EnergyLoss", m_energyLoss);
  declareProperty("Straggling", m_straggling);
  declareProperty("MostProbableEnergyLoss", m_MPV);
  declareProperty("StragglingScale", m_stragglingScale);
  declareProperty("DetailedEloss", m_detailedEloss);
  declareProperty("MultipleScatteringScale", m_scatteringScale);
  declareProperty("MaxPath", m_maxPath);
  declareProperty("MaxSteps", m_maxSteps);
  declareProperty("MSstepMax", m_layXmax);
  declareProperty("SimulationMode", m_simulation);
  declareProperty("SimMatEffUpdator", m_simMatUpdator);
  declareProperty("RandomNumberService", m_rndGenSvc, "Random number generator");
  declareProperty("RandomStreamName", m_randomEngineName, "Name of the random number stream");
}
 
// Destructor
 
Trk::STEP_Propagator::~STEP_Propagator() = default;
 
// Athena standard methods
// initialize
StatusCode Trk::STEP_Propagator::initialize() {
 
  // Read handle for AtlasFieldCacheCondObj
  ATH_CHECK(m_fieldCacheCondObjInputKey.initialize());
 
  if (!m_materialEffects) {  // override all material interactions
    m_multipleScattering = false;
    m_energyLoss = false;
    m_straggling = false;
  } else if (!m_energyLoss) {  // override straggling
    m_straggling = false;
  }
 
  if (m_simulation && m_simMatUpdator.retrieve().isFailure()) {
    ATH_MSG_WARNING("Simulation mode requested but material updator not found - no brem photon emission.");
  }
 
  if (m_simulation) {
    // get the random generator serice
    ATH_CHECK(m_rndGenSvc.retrieve());
    m_rngWrapper = m_rndGenSvc->getEngine(this, m_randomEngineName);
  }
 
  return StatusCode::SUCCESS;
}
 
// finalize
StatusCode Trk::STEP_Propagator::finalize() {
  return StatusCode::SUCCESS;
}
 
std::unique_ptr<Trk::NeutralParameters> Trk::STEP_Propagator::propagate(const Trk::NeutralParameters&,
                                                                        const Trk::Surface&,
                                                                        Trk::PropDirection,
                                                                        const Trk::BoundaryCheck&,
                                                                        bool) const {
  ATH_MSG_WARNING("[STEP_Propagator] STEP_Propagator does not handle neutral track parameters."
                  << "Use the StraightLinePropagator instead.");
  return nullptr;
}
 
// Main function for track parameters and covariance matrix propagation
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagate(
    const EventContext& ctx, const Trk::TrackParameters& trackParameters, const Trk::Surface& targetSurface,
    Trk::PropDirection propagationDirection, const Trk::BoundaryCheck& boundaryCheck,
    const MagneticFieldProperties& magneticFieldProperties, ParticleHypothesis particle, bool returnCurv,
    const Trk::TrackingVolume* tVol) const {
 
  // ATH_MSG_WARNING( "[STEP_Propagator] enter 1");
 
  double Jacobian[25];
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  cache.m_matupd_lastmom = trackParameters.momentum().mag();
  cache.m_matupd_lastpath = 0.;
  cache.m_matdump_lastpath = 0.;
 
  // no identified intersections needed/ no material dump / no path cache
  cache.m_identifiedParameters = nullptr;
  cache.m_matstates = nullptr;
  cache.m_extrapolationCache = nullptr;
  cache.m_hitVector = nullptr;
 
  return propagateRungeKuttaImpl(cache, true, trackParameters, targetSurface, propagationDirection,
                                 magneticFieldProperties, particle, boundaryCheck, Jacobian, returnCurv);
}
 
// Main function for track parameters and covariance matrix propagation
// with search of closest surface (ST)
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagate(
    const EventContext& ctx, const Trk::TrackParameters& trackParameters,
    std::vector<DestSurf>& targetSurfaces, Trk::PropDirection propagationDirection,
    const Trk::MagneticFieldProperties& magneticFieldProperties, ParticleHypothesis particle,
    std::vector<unsigned int>& solutions, double& path, bool usePathLimit, bool returnCurv,
    const Trk::TrackingVolume* tVol) const {
 
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  // no identified intersections needed/ no material dump
  cache.m_identifiedParameters = nullptr;
  cache.m_matstates = nullptr;
  cache.m_extrapolationCache = nullptr;
  cache.m_hitVector = nullptr;
 
  cache.m_matupd_lastmom = trackParameters.momentum().mag();
  cache.m_matupd_lastpath = 0.;
  cache.m_matdump_lastpath = 0.;
 
  // resolve path limit input
  if (path > 0.) {
    cache.m_propagateWithPathLimit = usePathLimit ? 1 : 0;
    cache.m_pathLimit = path;
    path = 0.;
  } else {
    cache.m_propagateWithPathLimit = 0;
    cache.m_pathLimit = -1.;
    path = 0.;
  }
  if (particle == Trk::neutron || particle == Trk::photon || particle == Trk::pi0 || particle == Trk::k0)
    return propagateNeutral(trackParameters, targetSurfaces, propagationDirection, solutions, path,
                            usePathLimit, returnCurv);
 
  return propagateRungeKutta(cache, true, trackParameters, targetSurfaces, propagationDirection,
                             magneticFieldProperties, particle, solutions, path, returnCurv);
}
 
// Main function for track parameters and covariance matrix propagation
// with search of closest surface and time info (ST)
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagateT(
    const EventContext& ctx, const Trk::TrackParameters& trackParameters,
    std::vector<DestSurf>& targetSurfaces, Trk::PropDirection propagationDirection,
    const Trk::MagneticFieldProperties& magneticFieldProperties, ParticleHypothesis particle,
    std::vector<unsigned int>& solutions, PathLimit& pathLim, TimeLimit& timeLim, bool returnCurv,
    const Trk::TrackingVolume* tVol, std::vector<Trk::HitInfo>*& hitVector) const {
 
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  // cache particle mass
  cache.m_particleMass = Trk::ParticleMasses::mass[particle];  // Get particle mass from ParticleHypothesis
 
  // cache input timing - for secondary track emission
  cache.m_timeIn = timeLim.time;
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  // no identified intersections needed/ no material dump
  cache.m_identifiedParameters = nullptr;
  cache.m_matstates = nullptr;
  cache.m_extrapolationCache = nullptr;
  cache.m_hitVector = hitVector;
 
  cache.m_matupd_lastmom = trackParameters.momentum().mag();
  cache.m_matupd_lastpath = 0.;
  cache.m_matdump_lastpath = 0.;
 
  // convert time/path limits into trajectory limit (in mm)
  double dMat = pathLim.x0Max - pathLim.x0Collected;
  double path =
      dMat > 0 && cache.m_matPropOK && cache.m_material->x0() > 0. ? dMat * cache.m_material->x0() : -1.;
 
  double dTim = timeLim.tMax - timeLim.time;
  double beta = 1.;
  if (dTim > 0.) {
    double mom = trackParameters.momentum().mag();
    beta = mom / std::sqrt(mom * mom + cache.m_particleMass * cache.m_particleMass);
  }
  double timMax = dTim > 0 ? dTim * beta * Gaudi::Units::c_light : -1.;
 
  if (timMax > 0. && timMax < path)
    path = timMax;
  bool usePathLimit = (path > 0.);
 
  // resolve path limit input
  if (path > 0.) {
    cache.m_propagateWithPathLimit = usePathLimit ? 1 : 0;
    cache.m_pathLimit = path;
    path = 0.;
  } else {
    cache.m_propagateWithPathLimit = 0;
    cache.m_pathLimit = -1.;
    path = 0.;
  }
 
  std::unique_ptr<Trk::TrackParameters> nextPar{};
 
  if (particle == Trk::neutron || particle == Trk::photon || particle == Trk::pi0 || particle == Trk::k0) {
    nextPar = propagateNeutral(trackParameters, targetSurfaces, propagationDirection, solutions, path,
                               usePathLimit, returnCurv);
  } else {
    nextPar = propagateRungeKutta(cache, true, trackParameters, targetSurfaces, propagationDirection,
                                  magneticFieldProperties, particle, solutions, path, returnCurv);
  }
  // update material path
  if (cache.m_matPropOK && cache.m_material->x0() > 0. && path > 0.) {
    pathLim.updateMat(path / cache.m_material->x0(), cache.m_material->averageZ(), 0.);
  }
  // return value
  timeLim.time += cache.m_timeOfFlight;
  return nextPar;
}
 
// Main function for track parameters and covariance matrix propagation
// with search of closest surface and material collection (ST)
 
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagateM(
    const EventContext& ctx, const Trk::TrackParameters& trackParameters,
    std::vector<DestSurf>& targetSurfaces, Trk::PropDirection propagationDirection,
    const Trk::MagneticFieldProperties& magneticFieldProperties, ParticleHypothesis particle,
    std::vector<unsigned int>& solutions, std::vector<const Trk::TrackStateOnSurface*>*& matstates,
    std::vector<std::pair<std::unique_ptr<Trk::TrackParameters>, int>>* intersections, double& path,
    bool usePathLimit, bool returnCurv, const Trk::TrackingVolume* tVol,
    Trk::ExtrapolationCache* extrapCache) const {
 
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  cache.m_matstates = matstates;
  cache.m_identifiedParameters = intersections;
  cache.m_extrapolationCache = extrapCache;
  cache.m_hitVector = nullptr;
 
  cache.m_matupd_lastmom = trackParameters.momentum().mag();
  cache.m_matupd_lastpath = 0.;
  cache.m_matdump_lastpath = 0.;
  cache.m_extrapolationCache = extrapCache;
 
  // switch on the detailed energy loss
  if (cache.m_extrapolationCache) {
    cache.m_detailedElossFlag = true;
  }
  // resolve path limit input
  if (path > 0.) {
    cache.m_propagateWithPathLimit = usePathLimit ? 1 : 0;
    cache.m_pathLimit = path;
    path = 0.;
  } else {
    cache.m_propagateWithPathLimit = 0;
    cache.m_pathLimit = -1.;
    path = 0.;
  }
  if (particle == Trk::neutron || particle == Trk::photon || particle == Trk::pi0 || particle == Trk::k0) {
    return propagateNeutral(trackParameters, targetSurfaces, propagationDirection, solutions, path,
                            usePathLimit, returnCurv);
  }
  return propagateRungeKutta(cache, true, trackParameters, targetSurfaces, propagationDirection,
                             magneticFieldProperties, particle, solutions, path, returnCurv);
}
 
// Main function for track parameters and covariance matrix propagation.
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagate(
    const EventContext& ctx,
    const Trk::TrackParameters& trackParameters,
    const Trk::Surface& targetSurface,
    Trk::PropDirection propagationDirection,
    const Trk::BoundaryCheck& boundaryCheck,
    const Trk::MagneticFieldProperties& magneticFieldProperties,
    std::optional<Trk::TransportJacobian>& jacobian,
    double&,
    ParticleHypothesis particle,
    bool returnCurv,
    const Trk::TrackingVolume* tVol) const {
 
  double Jacobian[25];
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  // no identified intersections needed/ no material dump
  cache.m_identifiedParameters = nullptr;
  cache.m_matstates = nullptr;
  cache.m_extrapolationCache = nullptr;
  cache.m_hitVector = nullptr;
 
  cache.m_matupd_lastmom = trackParameters.momentum().mag();
  cache.m_matupd_lastpath = 0.;
  cache.m_matdump_lastpath = 0.;
 
  std::unique_ptr<Trk::TrackParameters> parameters =
      propagateRungeKuttaImpl(cache, true, trackParameters, targetSurface, propagationDirection,
                              magneticFieldProperties, particle, boundaryCheck, Jacobian, returnCurv);
 
  if (parameters) {
    Jacobian[24] = Jacobian[20];
    Jacobian[23] = 0.;
    Jacobian[22] = 0.;
    Jacobian[21] = 0.;
    Jacobian[20] = 0.;
    jacobian = std::make_optional<Trk::TransportJacobian>(Jacobian);
  } else {
    jacobian.reset();
  }
 
  return parameters;
}
 
// Main function for track parameters propagation without covariance matrix
 
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagateParameters(
    const EventContext& ctx, const Trk::TrackParameters& trackParameters, const Trk::Surface& targetSurface,
    Trk::PropDirection propagationDirection, const Trk::BoundaryCheck& boundaryCheck,
    const Trk::MagneticFieldProperties& magneticFieldProperties, ParticleHypothesis particle, bool returnCurv,
    const Trk::TrackingVolume* tVol) const {
 
  double Jacobian[25];
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  // no identified intersections needed/ no material dump
  cache.m_identifiedParameters = nullptr;
  cache.m_matstates = nullptr;
  cache.m_hitVector = nullptr;
 
  return propagateRungeKuttaImpl(cache, false, trackParameters, targetSurface, propagationDirection,
                                 magneticFieldProperties, particle, boundaryCheck, Jacobian, returnCurv);
}
 
// Main function for track parameters propagation without covariance matrix.
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagateParameters(
    const EventContext& ctx,
    const Trk::TrackParameters& trackParameters,
    const Trk::Surface& targetSurface,
    Trk::PropDirection propagationDirection,
    const Trk::BoundaryCheck& boundaryCheck,
    const Trk::MagneticFieldProperties& magneticFieldProperties,
    std::optional<Trk::TransportJacobian>& jacobian,
    ParticleHypothesis particle,
    bool returnCurv,
    const Trk::TrackingVolume* tVol) const {
 
  double Jacobian[25];
 
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  // no identified intersections needed/ no material dump
  cache.m_identifiedParameters = nullptr;
  cache.m_matstates = nullptr;
  cache.m_extrapolationCache = nullptr;
  cache.m_hitVector = nullptr;
 
  std::unique_ptr<Trk::TrackParameters> parameters =
      propagateRungeKuttaImpl(cache, true, trackParameters, targetSurface, propagationDirection,
                              magneticFieldProperties, particle, boundaryCheck, Jacobian, returnCurv);
 
  if (parameters) {
    Jacobian[24] = Jacobian[20];
    Jacobian[23] = 0.;
    Jacobian[22] = 0.;
    Jacobian[21] = 0.;
    Jacobian[20] = 0.;
    jacobian = std::make_optional<Trk::TransportJacobian>(Jacobian);
  } else {
    jacobian.reset();
  }
 
  return parameters;
}
 
// Function for finding the intersection point with a surface
std::optional<Trk::TrackSurfaceIntersection> Trk::STEP_Propagator::intersect(
  const EventContext& ctx,
  const Trk::TrackParameters& trackParameters,
  const Trk::Surface& targetSurface,
  const Trk::MagneticFieldProperties& mft,
  ParticleHypothesis particle,
  const Trk::TrackingVolume* tVol) const {
 
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  cache.m_particle = particle;  // Store for later use
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  // no identified intersections needed/ no material dump
  cache.m_identifiedParameters = nullptr;
  cache.m_matstates = nullptr;
  cache.m_extrapolationCache = nullptr;
  cache.m_hitVector = nullptr;
 
  // Bfield mode
  mft.magneticFieldMode() == Trk::FastField ? cache.m_solenoid = true : cache.m_solenoid = false;
 
  // Check inputvalues
  if (cache.m_tolerance <= 0.) {
    return std::nullopt;
  }
  if (cache.m_momentumCutOff < 0.) {
    return std::nullopt;
  }
  if (std::abs(1. / trackParameters.parameters()[Trk::qOverP]) <= cache.m_momentumCutOff) {
    return std::nullopt;
  }
 
  // Check for empty volumes. If x != x then x is not a number.
  if (cache.m_matPropOK && ((cache.m_material->zOverAtimesRho() == 0.) || (cache.m_material->x0() == 0.) ||
                            (cache.m_material->zOverAtimesRho() != cache.m_material->zOverAtimesRho()))) {
    cache.m_matPropOK = false;
  }
 
  // double P[45];
  if (!Trk::RungeKuttaUtils::transformLocalToGlobal(false, trackParameters, cache.m_P)) {
      return std::nullopt;
  }
  double path = 0.;
 
  const Amg::Transform3D& T = targetSurface.transform();
  Trk::SurfaceType ty = targetSurface.type();
 
  if (ty == Trk::SurfaceType::Plane || ty == Trk::SurfaceType::Disc) {
    double s[4];
    double d = T(0, 3) * T(0, 2) + T(1, 3) * T(1, 2) + T(2, 3) * T(2, 2);
 
    if (d >= 0.) {
      s[0] = T(0, 2);
      s[1] = T(1, 2);
      s[2] = T(2, 2);
      s[3] = d;
    } else {
      s[0] = -T(0, 2);
      s[1] = -T(1, 2);
      s[2] = -T(2, 2);
      s[3] = -d;
    }
    if (!propagateWithJacobianImpl(cache, false, ty, s, cache.m_P, path)){
      return std::nullopt;
    }
  }
 
  else if (ty == Trk::SurfaceType::Line) {
 
    double s[6] = {T(0, 3), T(1, 3), T(2, 3), T(0, 2), T(1, 2), T(2, 2)};
    if (!propagateWithJacobianImpl(cache, false, ty, s, cache.m_P, path)) {
      return std::nullopt;
    }
  }
 
  else if (ty == Trk::SurfaceType::Cylinder) {
 
    const Trk::CylinderSurface* cyl = static_cast<const Trk::CylinderSurface*>(&targetSurface);
    double s[9] = {
        T(0, 3), T(1, 3), T(2, 3), T(0, 2), T(1, 2), T(2, 2), cyl->bounds().r(), Trk::alongMomentum, 0.};
    if (!propagateWithJacobianImpl(cache, false, ty, s, cache.m_P, path)) {
      return std::nullopt;
    }
  }
 
  else if (ty == Trk::SurfaceType::Cone) {
 
    double k = static_cast<const Trk::ConeSurface*>(&targetSurface)->bounds().tanAlpha();
    k = k * k + 1.;
    double s[9] = {T(0, 3), T(1, 3), T(2, 3), T(0, 2), T(1, 2), T(2, 2), k, Trk::alongMomentum, 0.};
    if (!propagateWithJacobianImpl(cache, false, ty, s, cache.m_P, path)) {
      return std::nullopt;
    }
  }
 
  else if (ty == Trk::SurfaceType::Perigee) {
 
    double s[6] = {T(0, 3), T(1, 3), T(2, 3), 0., 0., 1.};
    if (!propagateWithJacobianImpl(cache, false, ty, s, cache.m_P, path)) {
      return std::nullopt;
    }
  }
 
  else {  // presumably curvilinear
 
    double s[4];
    double d = T(0, 3) * T(0, 2) + T(1, 3) * T(1, 2) + T(2, 3) * T(2, 2);
 
    if (d >= 0.) {
      s[0] = T(0, 2);
      s[1] = T(1, 2);
      s[2] = T(2, 2);
      s[3] = d;
    } else {
      s[0] = -T(0, 2);
      s[1] = -T(1, 2);
      s[2] = -T(2, 2);
      s[3] = -d;
    }
    if (!propagateWithJacobianImpl(cache, false, ty, s, cache.m_P, path)) {
      return std::nullopt;
    }
  }
 
  Amg::Vector3D globalPosition(cache.m_P[0], cache.m_P[1], cache.m_P[2]);
  Amg::Vector3D direction(cache.m_P[3], cache.m_P[4], cache.m_P[5]);
  return std::make_optional<Trk::TrackSurfaceIntersection>(globalPosition, direction, path);
}
 
std::optional<Trk::TrackSurfaceIntersection>
Trk::STEP_Propagator::intersectSurface(
    const EventContext& ctx, const Trk::Surface& surface,
    const Trk::TrackSurfaceIntersection& trackIntersection, const double qOverP,
    const Trk::MagneticFieldProperties& mft,
    ParticleHypothesis particle) const {
 
  const Amg::Vector3D& origin = trackIntersection.position();
  const Amg::Vector3D& direction = trackIntersection.direction();
 
  auto perigeeSurface = PerigeeSurface(origin);
  perigeeSurface.setOwner(Trk::userOwn);  // tmp ones
 
  auto tmpTrackParameters =
      Trk::Perigee(0., 0., direction.phi(), direction.theta(), qOverP, perigeeSurface, std::nullopt);
 
  std::optional<Trk::TrackSurfaceIntersection> solution =
      qOverP == 0
          ? intersect(ctx, tmpTrackParameters, surface,
                      Trk::MagneticFieldProperties(Trk::NoField), particle)
          : intersect(ctx, tmpTrackParameters, surface, mft, particle, nullptr);
 
  return solution;
}
 
// Global positions calculation inside CylinderBounds
// if max step allowed > 0 -> propagate along momentum else propagate opposite momentum
void Trk::STEP_Propagator::globalPositions(const EventContext& ctx, std::deque<Amg::Vector3D>& positionsList,
                                           const Trk::TrackParameters& trackParameters,
                                           const Trk::MagneticFieldProperties& mft,
                                           const Trk::CylinderBounds& cylinderBounds, double maxStepSize,
                                           ParticleHypothesis particle,
                                           const Trk::TrackingVolume* tVol) const {
  Cache cache(ctx);
 
  // Get field cache object
  getFieldCacheObject(cache, ctx);
  setCacheFromProperties(cache);
  clearMaterialEffects(cache);
 
  cache.m_particle = particle;  // Store for later use
 
  // Check for tracking volume (materialproperties)
  cache.m_trackingVolume = tVol;
  cache.m_material = tVol;
  cache.m_matPropOK = tVol != nullptr;
 
  // Check for empty volumes. If x != x then x is not a number.
  if (cache.m_matPropOK && ((cache.m_material->zOverAtimesRho() == 0.) || (cache.m_material->x0() == 0.) ||
                            (cache.m_material->zOverAtimesRho() != cache.m_material->zOverAtimesRho()))) {
    cache.m_matPropOK = false;
  }
 
  mft.magneticFieldMode() == Trk::FastField ? cache.m_solenoid = true : cache.m_solenoid = false;
 
  // Check inputvalues
  if (cache.m_tolerance <= 0.)
    return;
 
  double PP[7];
  if (!Trk::RungeKuttaUtils::transformLocalToGlobal(false, trackParameters, PP))
    return;
 
  double maxPath = cache.m_maxPath;  // Max path allowed
  double dDir[3] = {0., 0., 0.};     // Start directions derivs. Zero in case of no RK steps
  double distanceStepped = 0.;
  double BG1[12] = {0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.};  // Bx, By, Bz, dBx/dx, dBx/dy, dBx/dz,
  // dBy/dx, dBy/dy, dBy/dz, dBz/dx, dBz/dy, dBz/dz
  bool firstStep = true;                                        // Poll B1, else recycle B4
  double path = 0.;                                             // path of the trajectory
  double radius2Max = cylinderBounds.r() * cylinderBounds.r();  // max. radius**2 of region
  double zMax = cylinderBounds.halflengthZ();                   // max. Z of region
  double radius2 = PP[0] * PP[0] + PP[1] * PP[1];               // Start radius**2
  double direction = PP[0] * PP[3] + PP[1] * PP[4];             // Direction
  double h = maxStepSize;                                       // max step allowed
 
  // Test position of the track
  if ((std::abs(PP[2]) > zMax) || (radius2 > radius2Max))
    return;
 
  // Store initial position
  Amg::Vector3D initialPosition(PP[0], PP[1], PP[2]);
  positionsList.push_back(initialPosition);
 
  bool perigee = false;
  if (std::abs(direction) < 0.00001) {
    perigee = true;
  }
 
  for (int i = 0; i != 2; ++i) {
    if (i) {
      if (perigee)
        return;
      h = -h;
    }
    double p[7] = {PP[0], PP[1], PP[2], PP[3], PP[4], PP[5], PP[6]};
 
    while (std::abs(path) < maxPath) {
      // Do the step.
      if (!rungeKuttaStep(cache, false, h, p, dDir, BG1, firstStep, distanceStepped))
        break;
      path = path + distanceStepped;
 
      // Keep h within max stepsize
      if (h > maxStepSize) {
        h = maxStepSize;
      } else if (h < -maxStepSize) {
        h = -maxStepSize;
      }
 
      // store current step
      Amg::Vector3D globalPosition(p[0], p[1], p[2]);
      if (!i) {
        positionsList.push_back(globalPosition);
      } else {
        positionsList.push_front(globalPosition);
      }
 
      // Test position of the track
      radius2 = p[0] * p[0] + p[1] * p[1];
      if ((std::abs(p[2]) > zMax) || (radius2 > radius2Max))
        break;
 
      // Test perigee
      if ((p[0] * p[3] + p[1] * p[4]) * direction < 0.) {
        if (i)
          return;
        perigee = true;
      }
    }
  }
}
 
// Main function for track propagation with or without jacobian
// with search of closest surface
std::unique_ptr<Trk::TrackParameters> Trk::STEP_Propagator::propagateRungeKutta(
    Cache& cache, bool errorPropagation, const Trk::TrackParameters& inputTrackParameters,
    std::vector<DestSurf>& targetSurfaces, Trk::PropDirection propagationDirection,
    const Trk::MagneticFieldProperties& mft, ParticleHypothesis particle,
    std::vector<unsigned int>& solutions, double& totalPath, bool returnCurv) const {
  // Store for later use
  cache.m_particle = particle;
  cache.m_charge = inputTrackParameters.charge();
  cache.m_inputThetaVariance = 0.;
 
  std::unique_ptr<Trk::TrackParameters> trackParameters{};
 
  // Bfield mode
  mft.magneticFieldMode() == Trk::FastField ? cache.m_solenoid = true : cache.m_solenoid = false;
 
  // Check inputvalues
  if (cache.m_tolerance <= 0.)
    return nullptr;
  if (cache.m_momentumCutOff < 0.)
    return nullptr;
 
  // Set momentum to 1e10 (straight line) and charge to + if q/p is zero
  if (inputTrackParameters.parameters()[Trk::qOverP] == 0) {
    trackParameters = createStraightLine(&inputTrackParameters);
    if (!trackParameters) {
      return nullptr;
    }
  } else {
    trackParameters.reset(inputTrackParameters.clone());
  }
 
  if (std::abs(1. / trackParameters->parameters()[Trk::qOverP]) <= cache.m_momentumCutOff) {
    return nullptr;
  }
 
  // Check for empty volumes. If x != x then x is not a number.
  if (cache.m_matPropOK && ((cache.m_material->zOverAtimesRho() == 0.) || (cache.m_material->x0() == 0.) ||
                            (cache.m_material->zOverAtimesRho() != cache.m_material->zOverAtimesRho()))) {
    cache.m_matPropOK = false;
  }
 
  if (errorPropagation && !trackParameters->covariance()) {
    errorPropagation = false;
  }
 
  if (cache.m_matPropOK && errorPropagation && cache.m_straggling)
    cache.m_stragglingVariance = 0.;
  cache.m_combinedCovariance.setZero();
  cache.m_covariance.setZero();
 
  if (errorPropagation || cache.m_matstates) {
    // this needs debugging
    cache.m_inputThetaVariance = trackParameters->covariance() ? (*trackParameters->covariance())(3, 3) : 0.;
    cache.m_combinedEloss.set(0., 0., 0., 0., 0., 0.);
    cache.m_combinedThickness = 0.;
  }
 
  // double P[45]; // Track parameters and jacobian
  if (!Trk::RungeKuttaUtils::transformLocalToGlobal(errorPropagation, *trackParameters, cache.m_P)) {
    return nullptr;
  }
 
  double path = 0.;
 
  // activate brem photon emission if required
  cache.m_brem = m_simulation && particle == Trk::electron && m_simMatUpdator;
 
  // loop while valid solutions
  bool validStep = true;
  totalPath = 0.;
  cache.m_timeOfFlight = 0.;
  // Common transformation for all surfaces (angles and momentum)
  double localp[5];
  double Jacobian[21];
  while (validStep) {
    // propagation to next surface
    validStep = propagateWithJacobian(cache, errorPropagation, targetSurfaces, cache.m_P,
                                      propagationDirection, solutions, path, totalPath);
    if (!validStep) {
      return nullptr;
    }
    if (propagationDirection * path <= 0.) {
      return nullptr;
    }
    totalPath += path;
    cache.m_timeOfFlight += cache.m_timeStep;
    if (cache.m_propagateWithPathLimit > 1 || cache.m_binMat) {
      // make sure that for sliding surfaces the result does not get distorted
      // return curvilinear parameters
      std::unique_ptr<Trk::CurvilinearParameters> cPar = nullptr;
      Trk::RungeKuttaUtils::transformGlobalToLocal(cache.m_P, localp);
      if (!errorPropagation) {
        cPar = std::make_unique<Trk::CurvilinearParameters>(
            Amg::Vector3D(cache.m_P[0], cache.m_P[1], cache.m_P[2]), localp[2], localp[3], localp[4]);
      } else {
        double useless[2];
        Trk::RungeKuttaUtils::transformGlobalToCurvilinear(true, cache.m_P, useless, Jacobian);
        AmgSymMatrix(5) measurementCovariance =
            Trk::RungeKuttaUtils::newCovarianceMatrix(Jacobian, *trackParameters->covariance());
        // Calculate multiple scattering and straggling covariance contribution.
        if (cache.m_matPropOK && (cache.m_multipleScattering || cache.m_straggling) &&
            std::abs(totalPath) > 0.) {
          covarianceContribution(cache, trackParameters.get(), totalPath, std::abs(1. / cache.m_P[6]),
                                 measurementCovariance);
        }
        cPar = std::make_unique<Trk::CurvilinearParameters>(
            Amg::Vector3D(cache.m_P[0], cache.m_P[1], cache.m_P[2]), localp[2], localp[3], localp[4],
            std::move(measurementCovariance));
      }
      // material collection : first iteration, bin material averaged
      // collect material
      if (cache.m_binMat && (cache.m_matstates || (errorPropagation && cache.m_extrapolationCache)) &&
          std::abs(totalPath - cache.m_matdump_lastpath) > 1.) {
        dumpMaterialEffects(cache, cPar.get(), totalPath);
      }
      return cPar;
    }
    if (cache.m_propagateWithPathLimit > 0)
      cache.m_pathLimit -= path;
    // boundary check
    // take into account that there may be many identical surfaces with different boundaries
    Amg::Vector3D gp(cache.m_P[0], cache.m_P[1], cache.m_P[2]);
    bool solution = false;
    std::vector<unsigned int> valid_solutions;
    valid_solutions.reserve(solutions.size());
 
    std::vector<unsigned int>::iterator iSol = solutions.begin();
    while (iSol != solutions.end()) {
      if (targetSurfaces[*iSol].first->isOnSurface(gp, targetSurfaces[*iSol].second, 0.001, 0.001)) {
        if (!solution) {
          Trk::RungeKuttaUtils::transformGlobalToLocal(cache.m_P, localp);
          if (returnCurv || targetSurfaces[*iSol].first->type() == Trk::SurfaceType::Cone) {
            Trk::RungeKuttaUtils::transformGlobalToCurvilinear(errorPropagation, cache.m_P, localp, Jacobian);
          } else
            Trk::RungeKuttaUtils::transformGlobalToLocal(targetSurfaces[*iSol].first, errorPropagation,
                                                         cache.m_P, localp, Jacobian);
          solution = true;
        }
        valid_solutions.push_back(*iSol);
      }
      ++iSol;
    }
    solutions = std::move(valid_solutions);
    if (solution)
      break;
  }
 
  if (solutions.empty()) {
    return nullptr;
  }
 
  // simulation mode : smear momentum
  if (m_simulation && cache.m_matPropOK) {
    double radDist = totalPath / cache.m_material->x0();
    smear(cache, localp[2], localp[3], trackParameters.get(), radDist);
  }
 
  std::unique_ptr<Trk::TrackParameters> onTargetSurf =
      (returnCurv || targetSurfaces[solutions[0]].first->type() == Trk::SurfaceType::Cone)
          ? nullptr
          : targetSurfaces[solutions[0]].first->createUniqueTrackParameters(
                localp[0], localp[1], localp[2], localp[3], localp[4], std::nullopt);
 
  if (!errorPropagation) {
    if (returnCurv || targetSurfaces[solutions[0]].first->type() == Trk::SurfaceType::Cone) {
      Amg::Vector3D gp(cache.m_P[0], cache.m_P[1], cache.m_P[2]);
      return std::make_unique<Trk::CurvilinearParameters>(gp, localp[2], localp[3], localp[4]);
    }
    return onTargetSurf;
  }
 
  // Errormatrix is included. Use Jacobian to calculate new covariance
  for (double i : Jacobian) {
    if (!Amg::saneCovarianceElement(i)) {
      return nullptr;
    }
  }
 
  AmgSymMatrix(5) measurementCovariance =
      Trk::RungeKuttaUtils::newCovarianceMatrix(Jacobian, *trackParameters->covariance());
  if (!Amg::hasPositiveOrZeroDiagElems(measurementCovariance))
    return nullptr;
 
  // Calculate multiple scattering and straggling covariance contribution.
  if (cache.m_matPropOK && (cache.m_multipleScattering || cache.m_straggling) && std::abs(totalPath) > 0.) {
    if (returnCurv || targetSurfaces[solutions[0]].first->type() == Trk::SurfaceType::Cone) {
      covarianceContribution(cache, trackParameters.get(), totalPath, std::abs(1. / cache.m_P[6]),
                             measurementCovariance);
    } else {
      covarianceContribution(cache, trackParameters.get(), totalPath, onTargetSurf.get(),
                             measurementCovariance);
    }
  }
 
  if (returnCurv || targetSurfaces[solutions[0]].first->type() == Trk::SurfaceType::Cone) {
    Amg::Vector3D gp(cache.m_P[0], cache.m_P[1], cache.m_P[2]);
    return std::make_unique<Trk::CurvilinearParameters>(gp, localp[2], localp[3], localp[4],
                                                        std::move(measurementCovariance));
  }
 
  // delete onTargetSurf;          // the covariance matrix can be just added instead of recreating ?
  return targetSurfaces[solutions[0]].first->createUniqueTrackParameters(
      localp[0], localp[1], localp[2], localp[3], localp[4], std::move(measurementCovariance));
}
 
// Runge Kutta main program for propagation with or without Jacobian
// with search of closest surface (ST)
bool Trk::STEP_Propagator::propagateWithJacobian(Cache& cache, bool errorPropagation,
                                                 std::vector<DestSurf>& sfs, double* P,
                                                 Trk::PropDirection propDir,
                                                 std::vector<unsigned int>& solutions, double& path,
                                                 double sumPath) const {
  double maxPath = cache.m_maxPath;  // Max path allowed
  double* pos = &P[0];               // Start coordinates
  double* dir = &P[3];               // Start directions
  double dDir[3] = {0., 0., 0.};     // Start directions derivs. Zero in case of no RK steps
  // int          targetPassed = 0;                 // how many times have we passed the target?
  double previousDistance = 0.;
  double distanceStepped = 0.;
  double BG1[12] = {0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0., 0.};  // Bx, By, Bz, dBx/dx, dBx/dy, dBx/dz,
  // dBy/dx, dBy/dy, dBy/dz, dBz/dx, dBz/dy, dBz/dz at first point
  bool firstStep = true;  // Poll BG1, else recycle BG4
  int steps = 0;
  path = 0.;              // path of the trajectory
  cache.m_timeStep = 0.;  // time separation corresponding to the trajectory
  double mom = 0.;        // need momentum and beta for timing
  double beta = 1.;       // need momentum and beta for timing
 
  // factor to stabilize iteration for soft tracks
  double helpSoft = 1.;
 
  // limit number of recovery attempts
  int restartLimit = 10;
 
  Amg::Vector3D position(P[0], P[1], P[2]);
  Amg::Vector3D direction0(P[3], P[4], P[5]);
 
  // binned material ?
  cache.m_binMat = nullptr;
  if (cache.m_trackingVolume && cache.m_trackingVolume->isAlignable()) {
    const Trk::AlignableTrackingVolume* aliTV =
        static_cast<const Trk::AlignableTrackingVolume*>(cache.m_trackingVolume);
    cache.m_binMat = aliTV->binnedMaterial();
  }
 
  // closest distance estimate
  // maintain count of oscilations and previous distance for each surface;
  // skip initial trivial solutions (input parameters at surface) - should be treated before call to the
  // propagator
  // !
  double tol = 0.001;
  solutions.clear();
  double distanceToTarget = propDir * maxPath;
  cache.m_currentDist.resize(sfs.size());  // keep size through the call
 
  int nextSf = sfs.size();
  int nextSfCand = nextSf;
  std::vector<DestSurf>::iterator sIter = sfs.begin();
  std::vector<DestSurf>::iterator sBeg = sfs.begin();
  unsigned int numSf = 0;
  unsigned int iCurr = 0;  // index for m_currentDist
  int startSf = -99;
  for (; sIter != sfs.end(); ++sIter) {
    Trk::DistanceSolution distSol = (*sIter).first->straightLineDistanceEstimate(position, direction0);
    double distEst = -propDir * maxPath;
    double dist1Est = distEst;
    if (distSol.numberOfSolutions() > 0) {
      distEst = distSol.first();
      dist1Est = distSol.first();
      if (distSol.numberOfSolutions() > 1 &&
          (std::abs(distEst) < tol || (propDir * distEst < -tol && propDir * distSol.second() > tol)))
        distEst = distSol.second();
    }
    // select input surfaces;
    // do not accept trivial solutions (at the surface)
    // but include them into further distance estimate (aca return to the same surface)
    if (distEst * propDir > -tol) {
      if (distSol.currentDistance() > 500.) {
        cache.m_currentDist[iCurr] = std::pair<int, std::pair<double, double>>(
            0, std::pair<double, double>(distEst, distSol.currentDistance(true)));
      } else {
        cache.m_currentDist[iCurr] = std::pair<int, std::pair<double, double>>(
            1, std::pair<double, double>(distEst, distSol.currentDistance(true)));
      }
      if (tol < propDir * distEst && propDir * distEst < propDir * distanceToTarget) {
        distanceToTarget = distEst;
        nextSf = iCurr;
      }
      ++numSf;
    } else {
      // save the nearest distance to surface
      cache.m_currentDist[iCurr] = std::pair<int, std::pair<double, double>>(
          -1, std::pair<double, double>(distSol.currentDistance(), distSol.currentDistance(true)));
    }
    if (std::abs(dist1Est) < tol)
      startSf = (int)iCurr;
    ++iCurr;
  }
 
  if (distanceToTarget == maxPath || numSf == 0)
    return false;
 
  // these do not change
  std::vector<std::pair<int, std::pair<double, double>>>::iterator vsBeg = cache.m_currentDist.begin();
  std::vector<std::pair<int, std::pair<double, double>>>::iterator vsEnd = cache.m_currentDist.end();
  const int num_vs_dist = cache.m_currentDist.size();
 
  // Set initial step length to 100mm or the distance to the target surface.
  double h = 0;
  double absPath = 0.;
  distanceToTarget > 100. ? h = 100. : distanceToTarget < -100. ? h = -100. : h = distanceToTarget;
 
  const Trk::IdentifiedMaterial* binIDMat = nullptr;
  // Adapt step size to the material binning : change of bin layer triggers dump of material effects
  if (cache.m_binMat) {
    const Trk::BinUtility* lbu = cache.m_binMat->layerBinUtility(position);
    if (lbu) {
      cache.m_currentLayerBin = cache.m_binMat->layerBin(position);
      binIDMat = cache.m_binMat->material(position);
      std::pair<size_t, float> dist2next = lbu->distanceToNext(position, propDir * direction0);
      if (dist2next.first < lbu->bins() && std::abs(dist2next.second) > 1. &&
          std::abs(dist2next.second) < std::abs(h)) {
        h = dist2next.second * propDir;
      }
      if (binIDMat)
        cache.m_material = binIDMat->first;
    }
  }
 
  // Step to within distanceTolerance, then do the rest as a Taylor expansion.
  // Keep distanceTolerance within [1 nanometer, 10 microns].
  // This means that no final Taylor expansions beyond 10 microns and no
  // Runge-Kutta steps less than 1 nanometer are allowed.
  double distanceTolerance = std::min(std::max(std::abs(distanceToTarget) * cache.m_tolerance, 1e-6), 1e-2);
 
  // bremstrahlung : sample if activated
  if (cache.m_brem) {
    mom = std::abs(1. / P[6]);
    sampleBrem(cache, mom);
  }
 
  while (numSf > 0 && (std::abs(distanceToTarget) > distanceTolerance ||
                       std::abs(path + distanceStepped) < tol)) {  // Step until within tolerance
    // Do the step. Stop the propagation if the energy goes below m_momentumCutOff
    if (!rungeKuttaStep(cache, errorPropagation, h, P, dDir, BG1, firstStep, distanceStepped)) {
      // emit brem photon before stopped ?
      if (cache.m_brem) {
        if (m_momentumCutOff < cache.m_bremEmitThreshold && m_simMatUpdator) {
          Amg::Vector3D position(P[0], P[1], P[2]);
          Amg::Vector3D direction(P[3], P[4], P[5]);
          m_simMatUpdator->recordBremPhoton(cache.m_timeIn + cache.m_timeOfFlight + cache.m_timeStep,
                                            m_momentumCutOff, cache.m_bremMom, position, direction,
                                            cache.m_particle);
          // the recoil can be skipped here
          for (int i = 0; i < 3; ++i)
            P[3 + i] = direction[i];
          // end recoil ( momentum not adjusted here ! continuous energy loss maintained for the moment)
        }
      }
      // collect material and update timing
      path = path + distanceStepped;
      // timing
      mom = std::abs(1. / P[6]);
      beta = mom / std::sqrt(mom * mom + cache.m_particleMass * cache.m_particleMass);
      cache.m_timeStep += distanceStepped / beta / Gaudi::Units::c_light;
 
      if (std::abs(distanceStepped) > 0.001) {
        cache.m_sigmaIoni = cache.m_sigmaIoni - cache.m_kazL * log(std::abs(distanceStepped));
      }
      // update straggling covariance
      if (errorPropagation && cache.m_straggling) {
        // 15% of the Radition moves the MOP value thus only 85% is accounted for by the Mean-MOP shift
        double sigTot2 = cache.m_sigmaIoni * cache.m_sigmaIoni + cache.m_sigmaRad * cache.m_sigmaRad;
        // /(beta*beta*p*p*p*p) transforms Var(E) to Var(q/p)
        double bp2 = beta * mom * mom;
        cache.m_stragglingVariance += sigTot2 / (bp2 * bp2) * distanceStepped * distanceStepped;
      }
      if (cache.m_matstates || errorPropagation) {
        cache.m_combinedEloss.update(
            cache.m_delIoni * distanceStepped, cache.m_sigmaIoni * std::abs(distanceStepped),
            cache.m_delRad * distanceStepped, cache.m_sigmaRad * std::abs(distanceStepped), cache.m_MPV);
      }
      if (cache.m_material && cache.m_material->x0() != 0.) {
        cache.m_combinedThickness += propDir * distanceStepped / cache.m_material->x0();
      }
 
      return false;
    }
    path = path + distanceStepped;
    absPath += std::abs(distanceStepped);
 
    // timing
    mom = std::abs(1. / P[6]);
    beta = mom / std::sqrt(mom * mom + cache.m_particleMass * cache.m_particleMass);
    cache.m_timeStep += distanceStepped / beta / Gaudi::Units::c_light;
 
    if (std::abs(distanceStepped) > 0.001)
      cache.m_sigmaIoni = cache.m_sigmaIoni - cache.m_kazL * log(std::abs(distanceStepped));
    // update straggling covariance
    if (errorPropagation && cache.m_straggling) {
      // 15% of the Radition moves the MOP value thus only 85% is accounted for by the Mean-MOP shift
      double sigTot2 = cache.m_sigmaIoni * cache.m_sigmaIoni + cache.m_sigmaRad * cache.m_sigmaRad;
      // /(beta*beta*p*p*p*p) transforms Var(E) to Var(q/p)
      double bp2 = beta * mom * mom;
      cache.m_stragglingVariance += sigTot2 / (bp2 * bp2) * distanceStepped * distanceStepped;
    }
    if (cache.m_matstates || errorPropagation) {
      cache.m_combinedEloss.update(
          cache.m_delIoni * distanceStepped, cache.m_sigmaIoni * std::abs(distanceStepped),
          cache.m_delRad * distanceStepped, cache.m_sigmaRad * std::abs(distanceStepped), cache.m_MPV);
    }
    if (cache.m_material && cache.m_material->x0() != 0.) {
      cache.m_combinedThickness += propDir * distanceStepped / cache.m_material->x0();
    }
 
    if (absPath > maxPath)
      return false;
 
    // path limit implemented
    if (cache.m_propagateWithPathLimit > 0 && cache.m_pathLimit <= path) {
      ++cache.m_propagateWithPathLimit;
      return true;
    }
 
    bool restart = false;
    // in case of problems, make shorter steps
    if (propDir * path < -tol || absPath - std::abs(path) > 10.) {
      helpSoft = std::abs(path) / absPath > 0.5 ? std::abs(path) / absPath : 0.5;
    }
 
    Amg::Vector3D position(P[0], P[1], P[2]);
    Amg::Vector3D direction(P[3], P[4], P[5]);
 
    // Adapt step size to the material binning : change of bin layer triggers dump of material effects
    float distanceToNextBin = h;  // default
    if (cache.m_binMat) {
      const Trk::BinUtility* lbu = cache.m_binMat->layerBinUtility(position);
      if (lbu) {
        size_t layerBin = cache.m_binMat->layerBin(position);
        const Trk::IdentifiedMaterial* iMat = cache.m_binMat->material(position);
        std::pair<size_t, float> dist2next = lbu->distanceToNext(position, propDir * direction);
        distanceToNextBin = dist2next.second;
        if (layerBin != cache.m_currentLayerBin) {  // step into new bin
          // check the overshoot
          std::pair<size_t, float> dist2previous = lbu->distanceToNext(position, -propDir * direction);
          float stepOver = dist2previous.second;
          double localp[5];
          Trk::RungeKuttaUtils::transformGlobalToLocal(P, localp);
          auto cPar = std::make_unique<Trk::CurvilinearParameters>(Amg::Vector3D(P[0], P[1], P[2]), localp[2],
                                                                   localp[3], localp[4]);
          if (cache.m_identifiedParameters) {
            if (binIDMat && binIDMat->second > 0 && !iMat) {  // exit from active layer
              cache.m_identifiedParameters->emplace_back(cPar->clone(), -binIDMat->second);
            } else if (binIDMat && binIDMat->second > 0 &&
                       (iMat->second == 0 || iMat->second == binIDMat->second)) {  // exit from active layer
              cache.m_identifiedParameters->emplace_back(cPar->clone(), -binIDMat->second);
            } else if (iMat && iMat->second > 0) {  // entry active layer
              cache.m_identifiedParameters->emplace_back(cPar->clone(), iMat->second);
            }
          }
          if (cache.m_hitVector) {
            double hitTiming = cache.m_timeIn + cache.m_timeOfFlight + cache.m_timeStep;
            if (binIDMat && binIDMat->second > 0 && !iMat) {  // exit from active layer
              cache.m_hitVector->emplace_back(cPar->uniqueClone(), hitTiming, -binIDMat->second, 0.);
            } else if (binIDMat && binIDMat->second > 0 &&
                       (iMat->second == 0 || iMat->second == binIDMat->second)) {  // exit from active layer
              cache.m_hitVector->emplace_back(cPar->uniqueClone(), hitTiming, -binIDMat->second, 0.);
            } else if (iMat && iMat->second > 0) {  // entry active layer
              cache.m_hitVector->emplace_back(cPar->uniqueClone(), hitTiming, iMat->second, 0.);
            }
          }
 
          cache.m_currentLayerBin = layerBin;
          binIDMat = iMat;
          if (binIDMat) {
            // change of material triggers update of the cache
            // @TODO Coverity complains about a possible NULL pointer dereferencing here
            //  because the code above does not explicitly forbid m_material to be NULL and m_material is used
            //  unchecked inside updateMaterialEffects.
            //  Can m_material be NULL at this point ?
            if (cache.m_material) {
              updateMaterialEffects(cache, mom, sin(direction.theta()), sumPath + path - stepOver);
            }
            cache.m_material = binIDMat->first;
          }
          // recalculate distance to next bin
          if (distanceToNextBin < h) {
            Amg::Vector3D probe = position + (distanceToNextBin + h) * propDir * direction;
            std::pair<size_t, float> d2n = lbu->distanceToNext(probe, propDir * direction);
            distanceToNextBin += d2n.second + h;
          }
        } else if (dist2next.first < lbu->bins() && std::abs(distanceToNextBin) < 0.01 &&
                   h > 0.01) {  // tolerance 10 microns ?
          double localp[5];
          Trk::RungeKuttaUtils::transformGlobalToLocal(P, localp);
          auto cPar = std::make_unique<Trk::CurvilinearParameters>(Amg::Vector3D(P[0], P[1], P[2]), localp[2],
                                                                   localp[3], localp[4]);
 
          const Trk::IdentifiedMaterial* nextMat = binIDMat;
          // need to know what comes next
          Amg::Vector3D probe = position + (distanceToNextBin + 0.01) * propDir * direction.normalized();
          nextMat = cache.m_binMat->material(probe);
 
          if (cache.m_identifiedParameters) {
            if (binIDMat && binIDMat->second > 0 && !nextMat) {  // exit from active layer
              cache.m_identifiedParameters->emplace_back(cPar->clone(), -binIDMat->second);
            } else if (binIDMat && binIDMat->second > 0 &&
                       (nextMat->second == 0 || nextMat->second == binIDMat->second)) {
              // exit from active layer
              cache.m_identifiedParameters->emplace_back(cPar->clone(), -binIDMat->second);
            } else if (nextMat && nextMat->second > 0) {  // entry active layer
              cache.m_identifiedParameters->emplace_back(cPar->clone(), nextMat->second);
            }
          }
          if (cache.m_hitVector) {
            double hitTiming = cache.m_timeIn + cache.m_timeOfFlight + cache.m_timeStep;
            if (binIDMat && binIDMat->second > 0 && !nextMat) {  // exit from active layer
              cache.m_hitVector->emplace_back(cPar->uniqueClone(), hitTiming, -binIDMat->second, 0.);
            } else if (binIDMat && binIDMat->second > 0 &&
                       (nextMat->second == 0 ||
                        nextMat->second == binIDMat->second)) {  // exit from active layer
              cache.m_hitVector->emplace_back(cPar->uniqueClone(), hitTiming, -binIDMat->second, 0.);
            } else if (nextMat && nextMat->second > 0) {  // entry active layer
              cache.m_hitVector->emplace_back(cPar->uniqueClone(), hitTiming, nextMat->second, 0.);
            }
          }
 
          cache.m_currentLayerBin = dist2next.first;
          if (binIDMat != nextMat) {  // change of material triggers update of the cache
            binIDMat = nextMat;
            if (binIDMat) {
              assert(cache.m_material);
              updateMaterialEffects(cache, mom, sin(direction.theta()), sumPath + path);
              cache.m_material = binIDMat->first;
            }
          }
          // recalculate distance to next bin
          std::pair<size_t, float> d2n = lbu->distanceToNext(probe, propDir * direction.normalized());
          distanceToNextBin += d2n.second + 0.01;
        }
        // TODO: trigger the update of material properties and recalculation of distance to the target sliding
        // surface
      }
    }
 
    // Calculate new distance to targets
    bool flipDirection = false;
    numSf = 0;
    nextSfCand = nextSf;
    double dev = direction0.dot(direction);
    std::vector<DestSurf>::iterator sIter = sBeg;
    std::vector<std::pair<int, std::pair<double, double>>>::iterator vsIter = vsBeg;
    int ic = 0;
    int numRestart = 0;
 
    if (cache.m_brem) {
      if (mom < cache.m_bremEmitThreshold && m_simMatUpdator) {
        // ST : strictly speaking, the emission point should be shifted backwards a bit
        // (mom-m_bremEmitThreshold) this seems to be a minor point
        m_simMatUpdator->recordBremPhoton(cache.m_timeIn + cache.m_timeOfFlight + cache.m_timeStep, mom,
                                          cache.m_bremMom, position, direction, cache.m_particle);
        cache.m_bremEmitThreshold = 0.;
      }
      if (mom < cache.m_bremSampleThreshold)
        sampleBrem(cache, cache.m_bremSampleThreshold);
    }
 
    for (; vsIter != vsEnd; ++vsIter) {
      if (restart) {
        ++numRestart;
        if (numRestart > restartLimit)
          return false;
 
        vsIter = vsBeg;
        ic = 0;
        sIter = sBeg;
        distanceToTarget = propDir * maxPath;
        nextSf = -1;
        nextSfCand = -1;
        restart = false;
        helpSoft = 1.;
      }
      if ((*vsIter).first != -1 &&
          (ic == nextSf || (*vsIter).first == 1 || nextSf < 0 || std::abs((*vsIter).second.first) < 500. ||
           std::abs(path) > 0.5 * std::abs((*vsIter).second.second))) {
        previousDistance = (*vsIter).second.first;
        Trk::DistanceSolution distSol =
            (*sIter).first->straightLineDistanceEstimate(position, propDir * direction);
        double distanceEst = -propDir * maxPath;
        if (distSol.numberOfSolutions() > 0) {
          distanceEst = distSol.first();
          if (distSol.numberOfSolutions() > 1 &&
              std::abs(distSol.first() * propDir + distanceStepped - previousDistance) >
                  std::abs(distSol.second() * propDir + distanceStepped - previousDistance)) {
            distanceEst = distSol.second();
          }
          // Peter Kluit: avoid jumping into other (distSol.first->second) distance solution for start surface
          // with negative distance solution
          //              negative distanceEst will trigger flipDirection = true and will iterate to the start
          //              surface this will lead to very similar positions for multiple propagator calls and
          //              many tiny X0 scatterers
          if (ic == startSf && distanceEst < 0 && distSol.first() > 0)
            distanceEst = distSol.first();
        }
        // eliminate close surface if path too small
        if (ic == nextSf && std::abs(distanceEst) < tol && std::abs(path) < tol) {
          (*vsIter).first = -1;
          vsIter = vsBeg;
          restart = true;
          distanceToTarget = maxPath;
          nextSf = -1;
          continue;
        }
 
        // If h and distance are in opposite directions, target is passed. Flip propagation direction
        // Verify if true intersection
        //  if (  h * propDir * distanceEst < 0. &&  std::abs(distanceEst)>distanceTolerance ) {
        if ((*vsIter).second.first * propDir * distanceEst < 0. &&
            std::abs(distanceEst) > distanceTolerance) {
          // verify change of sign in signedDistance ( after eliminating situations where this is meaningless
          // )
          if (!distSol.signedDistance() || std::abs(distSol.currentDistance(true)) < tol ||
              std::abs((*vsIter).second.second) < tol ||
              (*vsIter).second.second * distSol.currentDistance(true) < 0) {  // true intersection
            if (ic == nextSf) {
              ((*vsIter).first)++;
              // eliminate surface if diverging
              if ((*vsIter).first > 3) {
                helpSoft = fmax(0.05, 1. - 0.05 * (*vsIter).first);
                if ((*vsIter).first > 20)
                  helpSoft = 1. / (*vsIter).first;
              }
              // take care of eliminating when number of flips even - otherwise it may end up at the start !
              if ((*vsIter).first > 50 && h * propDir > 0) {
                // std::abs(distanceEst) >= std::abs(previousDistance) )  {
                (*vsIter).first = -1;
                vsIter = vsBeg;
                restart = true;
                continue;
              }
              if ((*vsIter).first != -1)
                flipDirection = true;
            } else if (std::abs((*vsIter).second.second) > tol &&
                       std::abs(distSol.currentDistance(true)) > tol) {
              // here we need to compare with distance from current closest
              if (ic > nextSf && nextSf != -1) {  // easy case, already calculated
                if (propDir * distanceEst < (cache.m_currentDist.at(nextSf)).second.first - tol) {
                  if ((*vsIter).first != -1) {
                    ((*vsIter).first)++;
                    flipDirection = true;
                    nextSf = ic;
                  }
                }
              } else if (distanceToTarget >
                         0.) {  // set as nearest (if not iterating already), will be rewritten later
                if ((*vsIter).first != -1) {
                  ((*vsIter).first)++;
                  flipDirection = true;
                  nextSf = ic;
                }
              }
            }
          } else if (ic == nextSf) {
            vsIter = vsBeg;
            restart = true;
            continue;
          }
        }
 
        // save current distance to surface
        (*vsIter).second.first = propDir * distanceEst;
        (*vsIter).second.second = distSol.currentDistance(true);
 
        //  find closest surface: the step may have been beyond several surfaces
        //  from all surfaces with 'negative' distance, consider only the one currently designed as 'closest'
        //  mw  if ((*vsIter).first!=-1 && ( distanceEst>-tol || ic==nextSf ) ) {
        if ((*vsIter).first != -1 && (distanceEst > 0. || ic == nextSf)) {
          ++numSf;
          if (distanceEst < std::abs(distanceToTarget)) {
            distanceToTarget = propDir * distanceEst;
            nextSfCand = ic;
          }
        }
      } else if (std::abs(path) > std::abs((*vsIter).second.second) || dev < 0.985 ||
                 nextSf < 0) {  // keep an eye on surfaces with negative distance; tracks are curved !
        Trk::DistanceSolution distSol =
            (*sIter).first->straightLineDistanceEstimate(position, propDir * direction);
        double distanceEst = -propDir * maxPath;
        if (distSol.numberOfSolutions() > 0) {
          distanceEst = distSol.first();
        }
        // save current distance to surface
        (*vsIter).second.first = propDir * distanceEst;
        (*vsIter).second.second = distSol.currentDistance(true);
        // reactivate surface
        if (distanceEst > tol && distanceEst < maxPath) {
          (*vsIter).first = 0;
        } else {
          (*vsIter).second.first = distSol.currentDistance() + std::abs(path);
        }
        if ((*vsIter).first != -1 && distanceEst > 0.) {
          ++numSf;
          if (distanceEst < std::abs(distanceToTarget)) {
            distanceToTarget = propDir * distanceEst;
            nextSfCand = ic;
          }
        }
      }
      // additional protection - return to the same surface
      // eliminate the surface and restart the search
      // 04/10/10 ST:infinite loop due to distanceTolerance>tol fixed;
      if (std::abs(distanceToTarget) <= distanceTolerance && path * propDir < distanceTolerance) {
        (*vsIter).first = -1;
        vsIter = vsBeg;
        restart = true;
        continue;
      }
      ++sIter;
      ++ic;
    }
    // if next closest not found, propagation failed
    if (nextSf < 0 && nextSfCand < 0)
      return false;
    // flip direction
    if (flipDirection) {
      // Out of bounds protection
      if (nextSf < 0 || nextSf >= num_vs_dist)
        return false;
      distanceToTarget = (*(vsBeg + nextSf)).second.first;
      h = -h;
    } else if (nextSfCand != nextSf) {
      nextSf = nextSfCand;
      // Out of bounds protection
      if (nextSf < 0 || nextSf >= num_vs_dist)
        return false;
      if (cache.m_currentDist[nextSf].first < 3)
        helpSoft = 1.;
    }
 
    // don't step beyond surfaces - adjust step
    if (std::abs(h) > std::abs(distanceToTarget))
      h = distanceToTarget;
 
    // don't step beyond bin boundary - adjust step
    if (cache.m_binMat && std::abs(h) > std::abs(distanceToNextBin) + 0.001) {
      if (distanceToNextBin > 0) {  // TODO : investigate source of negative distance in BinningData
        h = distanceToNextBin * propDir;
      }
    }
 
    if (helpSoft < 1.)
      h *= helpSoft;
 
    // don't step much beyond path limit
    if (cache.m_propagateWithPathLimit > 0 && h > cache.m_pathLimit)
      h = cache.m_pathLimit + tol;
 
    // Abort if maxPath is reached
    if (std::abs(path) > maxPath)
      return false;
 
    if (steps++ > cache.m_maxSteps)
      return false;  // Too many steps, something is wrong
  }
 
  if (!numSf)
    return false;
 
  // Use Taylor expansions to step the remaining distance (typically microns).
  path = path + distanceToTarget;
 
  // timing
  mom = std::abs(1. / P[6]);
  beta = mom / std::sqrt(mom * mom + cache.m_particleMass * cache.m_particleMass);
  cache.m_timeStep += distanceToTarget / beta / Gaudi::Units::c_light;
 
  // pos = pos + h*dir + 1/2*h*h*dDir. Second order Taylor expansion.
  pos[0] = pos[0] + distanceToTarget * (dir[0] + 0.5 * distanceToTarget * dDir[0]);
  pos[1] = pos[1] + distanceToTarget * (dir[1] + 0.5 * distanceToTarget * dDir[1]);
  pos[2] = pos[2] + distanceToTarget * (dir[2] + 0.5 * distanceToTarget * dDir[2]);
 
  // dir = dir + h*dDir. First order Taylor expansion (Euler).
  dir[0] = dir[0] + distanceToTarget * dDir[0];
  dir[1] = dir[1] + distanceToTarget * dDir[1];
  dir[2] = dir[2] + distanceToTarget * dDir[2];
 
  // Normalize dir
  double norm = 1. / std::sqrt(dir[0] * dir[0] + dir[1] * dir[1] + dir[2] * dir[2]);
  dir[0] = norm * dir[0];
  dir[1] = norm * dir[1];
  dir[2] = norm * dir[2];
  P[42] = dDir[0];
  P[43] = dDir[1];
  P[44] = dDir[2];
 
  // collect all surfaces with distance below tolerance
  std::vector<std::pair<int, std::pair<double, double>>>::iterator vsIter = vsBeg;
 
  int index = 0;
  for (; vsIter != vsEnd; ++vsIter) {
    if ((*vsIter).first != -1 && propDir * (*vsIter).second.first >= propDir * distanceToTarget - tol &&
        propDir * (*vsIter).second.first < 0.01 && index != nextSf) {
      solutions.push_back(index);
    }
    if (index == nextSf)
      solutions.push_back(index);
    ++index;
  }
 
  return true;
}
 
// dump material effects
void Trk::STEP_Propagator::dumpMaterialEffects(Cache& cache, const Trk::CurvilinearParameters* parms,
                                               double path) const {
 
  // kinematics
  double mom = parms->momentum().mag();
 
  // first update to make sure all material counted
  updateMaterialEffects(cache, mom, sin(parms->momentum().theta()), path);
 
  if (cache.m_extrapolationCache) {
    cache.m_extrapolationCache->updateX0(cache.m_combinedThickness);
    cache.m_extrapolationCache->updateEloss(
        cache.m_combinedEloss.meanIoni(), cache.m_combinedEloss.sigmaIoni(), cache.m_combinedEloss.meanRad(),
        cache.m_combinedEloss.sigmaRad());
  }
  // output
  if (cache.m_matstates) {
    auto eloss = !m_detailedEloss
                     ? std::make_unique<Trk::EnergyLoss>(cache.m_combinedEloss.deltaE(),
                                                         cache.m_combinedEloss.sigmaDeltaE())
                     : std::make_unique<Trk::EnergyLoss>(
                           cache.m_combinedEloss.deltaE(), cache.m_combinedEloss.sigmaDeltaE(),
                           cache.m_combinedEloss.sigmaDeltaE(), cache.m_combinedEloss.sigmaDeltaE(),
                           cache.m_combinedEloss.meanIoni(), cache.m_combinedEloss.sigmaIoni(),
                           cache.m_combinedEloss.meanRad(), cache.m_combinedEloss.sigmaRad(), path);
 
    auto sa = Trk::ScatteringAngles(0., 0., std::sqrt(cache.m_covariance(2, 2)),
                                    std::sqrt(cache.m_covariance(3, 3)));
 
    auto cvlTP = parms->uniqueClone();
    auto mefot = std::make_unique<Trk::MaterialEffectsOnTrack>(cache.m_combinedThickness, sa,
                                                               std::move(eloss), cvlTP->associatedSurface());
 
    cache.m_matstates->push_back(new TrackStateOnSurface(nullptr, std::move(cvlTP), std::move(mefot)));
  }
 
  cache.m_matdump_lastpath = path;
 
  // clean-up
  cache.m_combinedCovariance += cache.m_covariance;
  cache.m_covariance.setZero();
  cache.m_combinedThickness = 0.;
  cache.m_combinedEloss.set(0., 0., 0., 0., 0., 0.);
}
 
// Smear momentum ( simulation mode )
void Trk::STEP_Propagator::smear(Cache& cache, double& phi, double& theta, const Trk::TrackParameters* parms,
                                 double radDist) const {
  if (cache.m_particle == Trk::geantino)
    return;
  if (!parms)
    return;
 
  if (!cache.m_randomEngine) {
    cache.m_randomEngine = getRandomEngine(cache.m_ctx);
  }
 
  // Calculate polar angle
  double particleMass = Trk::ParticleMasses::mass[cache.m_particle];  // Get particle mass from
                                                                      // ParticleHypothesis
  double momentum = parms->momentum().mag();
  double energy = std::sqrt(momentum * momentum + particleMass * particleMass);
  double beta = momentum / energy;
  double th = std::sqrt(2.) * 15. * std::sqrt(radDist) / (beta * momentum) *
              CLHEP::RandGauss::shoot(cache.m_randomEngine);  // Moliere
  // double th = (sqrt(2.)*13.6*std::sqrt(radDist)/(beta*momentum)) *
  // (1.+0.038*log(radDist/(beta*beta))) * m_gaussian->shoot(); //Highland
 
  // Calculate azimuthal angle
  double ph = 2. * M_PI * CLHEP::RandFlat::shoot(cache.m_randomEngine);
 
  Amg::Transform3D rot(Amg::AngleAxis3D(-theta, Amg::Vector3D(0., 1., 0.)) *
                       Amg::AngleAxis3D(-phi, Amg::Vector3D(0., 0., 1.)));
  Amg::Vector3D dir0(0., 0., 1.);
  Amg::Vector3D rotated = rot.inverse() * Amg::AngleAxis3D(ph, Amg::Vector3D(0., 0., 1.)) *
                          Amg::AngleAxis3D(th, Amg::Vector3D(0., 1., 0.)) * dir0;
 
  theta = rotated.theta();
  phi = rotated.phi();
}
 
// Sample momentum of brem photon ( simulation mode )
void Trk::STEP_Propagator::sampleBrem(Cache& cache, double mom) const {
  if (!cache.m_randomEngine) {
    cache.m_randomEngine = getRandomEngine(cache.m_ctx);
  }
  double rndx = CLHEP::RandFlat::shoot(cache.m_randomEngine);
  double rnde = CLHEP::RandFlat::shoot(cache.m_randomEngine);
 
  // sample visible fraction of the mother momentum taken according to 1/f
  double eps = cache.m_momentumCutOff / mom;
  cache.m_bremMom = pow(eps, pow(rndx, exp(1.))) * mom;  // adjustment here ?
  cache.m_bremSampleThreshold = mom - cache.m_bremMom;
  cache.m_bremEmitThreshold = mom - rnde * cache.m_bremMom;
}
 
void Trk::STEP_Propagator::getFieldCacheObject(Cache& cache, const EventContext& ctx) const {
  SG::ReadCondHandle<AtlasFieldCacheCondObj> readHandle{m_fieldCacheCondObjInputKey, ctx};
  const AtlasFieldCacheCondObj* fieldCondObj{*readHandle};
  if (fieldCondObj == nullptr) {
    ATH_MSG_ERROR("extrapolate: Failed to retrieve AtlasFieldCacheCondObj with key "
                  << m_fieldCacheCondObjInputKey.key());
    return;
  }
  fieldCondObj->getInitializedCache(cache.m_fieldCache);
}
 
CLHEP::HepRandomEngine*
Trk::STEP_Propagator::getRandomEngine (const EventContext& ctx) const
{
  if (!m_simulation || !m_rngWrapper) {
    return nullptr;
  }
  if (m_rngWrapper->evtSeeded(ctx) != ctx.evt()) {
    // Ok, the wrappers are unique to this algorithm and a given slot,
    // so cannot be accessed concurrently.
    ATHRNG::RNGWrapper* wrapper_nc ATLAS_THREAD_SAFE = m_rngWrapper;
    wrapper_nc->setSeed (this->name(), ctx);
  }
  return m_rngWrapper->getEngine (ctx);
}