CDCRobustSZFitter.cc

/**************************************************************************
 * BASF2 (Belle Analysis Framework 2)                                     *
 * Copyright(C) 2016 - Belle II Collaboration                             *
 *                                                                        *
 * Author: The Belle II Collaboration                                     *
 * Contributors: Oliver Frost, Nils Braun                                 *
 *                                                                        *
 * This software is provided "as is" without any warranty.                *
 **************************************************************************/
#include <tracking/trackFindingCDC/fitting/CDCRobustSZFitter.h>
 
#include <tracking/trackFindingCDC/fitting/CDCSZFitter.h>
 
#include <tracking/trackFindingCDC/fitting/CDCSZObservations.h>
 
#include <tracking/trackFindingCDC/eventdata/trajectories/CDCTrajectorySZ.h>
 
#include <tracking/trackFindingCDC/numerics/Median.h>
#include <tracking/trackFindingCDC/numerics/WithWeight.h>
 
using namespace Belle2;
using namespace TrackFindingCDC;
 
CDCTrajectorySZ CDCRobustSZFitter::fitUsingSimplifiedTheilSen(const CDCSZObservations& observationsSZ) const
{
  // This seems to be some other algorithm
 
 
  CDCTrajectorySZ trajectorySZ;
  CDCSZFitter szFitter;
 
  if (observationsSZ.size() > 4) {
    CDCSZObservations observationsSZFiltered;
 
    double meanTanLambda = 0;
    double meanStartZ = 0;
 
    for (unsigned int i = 0; i < observationsSZ.size(); i++) {
      for (unsigned int j = 0; j < observationsSZ.size(); j++) {
        if (i != j) {
          observationsSZFiltered.fill(observationsSZ.getS(j),
                                      observationsSZ.getZ(j),
                                      observationsSZ.getWeight(j));
        }
      } // for j
 
      szFitter.update(trajectorySZ, observationsSZFiltered);
      meanTanLambda += trajectorySZ.getTanLambda();
      meanStartZ += trajectorySZ.getZ0();
    } // for i
 
    return CDCTrajectorySZ(meanTanLambda / observationsSZ.size(),
                           meanStartZ / observationsSZ.size());
  } else {
    return CDCTrajectorySZ::basicAssumption();
  }
}
 
CDCTrajectorySZ CDCRobustSZFitter::fitTheilSen(const CDCSZObservations& szObservations) const
{
  std::vector<double> tanLambdas;
  tanLambdas.reserve(szObservations.size() * (szObservations.size() - 1) / 2);
  for (unsigned int i = 0; i < szObservations.size(); i++) {
    for (unsigned int j = i + 1; j < szObservations.size(); j++) {
      double s1 = szObservations.getS(i);
      double s2 = szObservations.getS(j);
      if (s1 == s2) continue;
      double z1 = szObservations.getZ(i);
      double z2 = szObservations.getZ(j);
      tanLambdas.push_back((z2 - z1) / (s2 - s1));
    }
  }
 
  const double tanLambda = median(std::move(tanLambdas));
  const double z0 = getMedianZ0(szObservations, tanLambda);
 
  CDCTrajectorySZ trajectorySZ(tanLambda, z0);
  trajectorySZ.setNDF(szObservations.size());
  return trajectorySZ;
}
 
CDCTrajectorySZ CDCRobustSZFitter::fitWeightedTheilSen(const CDCSZObservations& szObservations) const
{
  std::vector<WithWeight<double> > weightedTanLambdas;
  Weight totalWeight = 0;
  weightedTanLambdas.reserve(szObservations.size() * (szObservations.size() - 1) / 2);
  for (unsigned int i = 0; i < szObservations.size(); i++) {
    for (unsigned int j = i + 1; j < szObservations.size(); j++) {
      double s1 = szObservations.getS(i);
      double s2 = szObservations.getS(j);
      if (s1 == s2) continue;
      double z1 = szObservations.getZ(i);
      double z2 = szObservations.getZ(j);
 
      double w1 = szObservations.getWeight(i);
      double w2 = szObservations.getWeight(j);
 
      // Longer legs receive proportionally longer weight.
      Weight weight = std::abs(s2 - s1) * hypot2(w1, w2);
      weightedTanLambdas.emplace_back((z2 - z1) / (s2 - s1),  weight);
      totalWeight += weight;
    }
  }
 
  for (WithWeight<double>& weightedTanLambda : weightedTanLambdas) {
    weightedTanLambda.weight() /= totalWeight;
  }
 
  const double tanLambda = weightedMedian(std::move(weightedTanLambdas));
  const double z0 = getMedianZ0(szObservations, tanLambda);
 
  CDCTrajectorySZ trajectorySZ(tanLambda, z0);
  trajectorySZ.setNDF(szObservations.size());
  return trajectorySZ;
}
 
double CDCRobustSZFitter::getMedianZ0(const CDCSZObservations& szObservations, double tanLambda) const
{
  std::vector<double> z0s;
  z0s.reserve(szObservations.size());
  for (unsigned int i = 0; i < szObservations.size(); i++) {
    double s = szObservations.getS(i);
    double z = szObservations.getZ(i);
    z0s.push_back(z - s * tanLambda);
  }
  const double z0 = median(std::move(z0s));
  return z0;
}