KarimakisMethod.cc

/**************************************************************************
 * basf2 (Belle II Analysis Software Framework)                           *
 * Author: The Belle II Collaboration                                     *
 *                                                                        *
 * See git log for contributors and copyright holders.                    *
 * This file is licensed under LGPL-3.0, see LICENSE.md.                  *
 **************************************************************************/
#include <tracking/trackFindingCDC/fitting/KarimakisMethod.h>
 
#include <tracking/trackFindingCDC/fitting/EigenObservationMatrix.h>
#include <tracking/trackFindingCDC/fitting/CDCObservations2D.h>
 
#include <tracking/trackFindingCDC/eventdata/trajectories/CDCTrajectory2D.h>
 
#include <tracking/trackFindingCDC/geometry/UncertainPerigeeCircle.h>
#include <tracking/trackFindingCDC/geometry/PerigeeParameters.h>
#include <tracking/trackFindingCDC/geometry/Vector2D.h>
 
#include <Eigen/Core>
 
using namespace Belle2;
using namespace TrackFindingCDC;
 
KarimakisMethod::KarimakisMethod()
  : m_lineConstrained(false)
{
}
 
void KarimakisMethod::update(CDCTrajectory2D& trajectory2D,
                             CDCObservations2D& observations2D) const
{
  size_t nObservations = observations2D.size();
  trajectory2D.clear();
  if (not nObservations) return;
 
  Vector2D ref = observations2D.getCentralPoint();
  observations2D.passiveMoveBy(ref);
 
  UncertainPerigeeCircle perigeeCircle = fitInternal(observations2D);
 
  double frontX = observations2D.getX(0);
  double frontY = observations2D.getY(0);
  Vector2D frontPos(frontX, frontY);
 
  double backX = observations2D.getX(nObservations - 1);
  double backY = observations2D.getY(nObservations - 1);
  Vector2D backPos(backX, backY);
 
  Vector2D overPos(0, 0);
  double totalPerps = (perigeeCircle->arcLengthBetween(frontPos, overPos) +
                       perigeeCircle->arcLengthBetween(overPos, backPos));
 
  if (totalPerps < 0) {
    perigeeCircle.reverse();
  }
 
  trajectory2D.setLocalOrigin(ref);
  trajectory2D.setLocalCircle(perigeeCircle);
}
 
 
 
 
namespace {
  constexpr size_t iW = 0;
  constexpr size_t iX = 1;
  constexpr size_t iY = 2;
  constexpr size_t iR2 = 3;
 
  UncertainPerigeeCircle fitKarimaki(const double /*sw*/,
                                     const Eigen::Matrix< double, 4, 1 >& a,
                                     const Eigen::Matrix< double, 4, 4 >& c,
                                     bool lineConstrained = false)
  {
    double q1, q2 = 0.0;
    if (lineConstrained) {
      q1 = c(iX, iY);
      q2 = c(iX, iX) - c(iY, iY);
    } else {
      q1 = c(iX, iY) * c(iR2, iR2) - c(iX, iR2) * c(iY, iR2);
      q2 = (c(iX, iX) - c(iY, iY)) * c(iR2, iR2) - c(iX, iR2) * c(iX, iR2) + c(iY, iR2) * c(iY, iR2);
    }
 
    double phi = 0.5 * atan2(2. * q1, q2);
 
    double sinphi = sin(phi);
    double cosphi = cos(phi);
 
    double curv, I = 0.0;
    if (lineConstrained) {
      curv = 0.0; //line
      I = sinphi * a(iX) - cosphi * a(iY);
 
    } else {
      double kappa = (sinphi * c(iX, iR2) - cosphi * c(iY, iR2)) / c(iR2, iR2);
      double delta = -kappa * a(iR2) + sinphi * a(iX) - cosphi * a(iY);
      curv = 2. * kappa / sqrt(1. - 4. * delta * kappa);
      I = 2. * delta / (1. + sqrt(1. - 4. * delta * kappa));
 
    }
 
    // Karimaki uses the opposite sign for phi in contrast to the convention of this framework !!!
    phi += phi > 0 ? -M_PI : M_PI;
    return UncertainPerigeeCircle(curv, phi, I);
 
  }
 
 
 
 
 
  double calcChi2Karimaki(const PerigeeCircle& parameters,
                          const double sw,
                          const Eigen::Matrix< double, 4, 4 >& c,
                          bool lineConstrained = false)
  {
    // Karimaki uses the opposite sign for phi in contrast to the convention of this framework !!!
    const Vector2D vecPhi = -parameters.tangential();
 
    const double cosphi = vecPhi.x();
    const double sinphi = vecPhi.y();
 
    if (lineConstrained) {
      double chi2 = sw * (sinphi * sinphi * c(iX, iX) - 2. * sinphi * cosphi * c(iX, iY) + cosphi * cosphi * c(iY, iY));
      return chi2;
    } else {
      // Terminology Karimaki used in the paper
      const double rho = parameters.curvature();
      const double d = parameters.impact();
 
      const double u = 1 + d * rho;
      const double kappa = 0.5 * rho / u;
 
      double chi2 =  sw * u * u * (sinphi * sinphi * c(iX, iX) - 2. * sinphi * cosphi * c(iX, iY) + cosphi * cosphi * c(iY,
                                   iY) - kappa * kappa * c(iR2, iR2));
      return chi2;
    }
 
  }
 
 
 
  PerigeePrecision calcPrecisionKarimaki(const PerigeeCircle& parameters,
                                         const Eigen::Matrix< double, 4, 4 >& s,
                                         bool lineConstrained = false)
  {
    PerigeePrecision perigeePrecision;
 
    const double curv = parameters.curvature();
    const double I =  parameters.impact();
 
    // Karimaki uses the opposite sign for phi in contrast to the convention of this framework !!!
    const Vector2D vecPhi = -parameters.tangential();
 
    // Ternminology Karimaki using in the paper
    const double cosphi = vecPhi.x();
    const double sinphi = vecPhi.y();
 
    const double ssphi = sinphi * sinphi;
    const double scphi = sinphi * cosphi;
    const double ccphi = cosphi * cosphi;
 
    const double rho = curv;
    const double d = I;
 
    const double u = 1. + rho * d;
 
    using namespace NPerigeeParameterIndices;
    if (lineConstrained) {
      perigeePrecision(c_Curv, c_Curv) = 0.;
      perigeePrecision(c_Curv, c_Phi0) = 0.;
      perigeePrecision(c_Curv, c_I) = 0.;
      perigeePrecision(c_Phi0, c_Curv) = 0.;
      perigeePrecision(c_I, c_Curv) = 0.;
 
      perigeePrecision(c_Phi0, c_Phi0) = ccphi * s(iX, iX) + 2. * scphi * s(iX, iY) + ssphi * s(iY, iY);
      perigeePrecision(c_Phi0, c_I) = -(cosphi * s(iX) + sinphi * s(iY));
      perigeePrecision(c_I, c_Phi0) = perigeePrecision(c_Phi0, c_I);
      perigeePrecision(c_I, c_I) = s(iW);
 
    } else {
      double sa = sinphi * s(iX) - cosphi * s(iY);
      double sb = cosphi * s(iX) + sinphi * s(iY);
      double sc = (ssphi - ccphi) * s(iX, iY) + scphi * (s(iX, iX) - s(iY, iY));
 
      double sd = sinphi * s(iX, iR2) - cosphi * s(iY, iR2);
 
      double saa = ssphi * s(iX, iX) - 2. * scphi * s(iX, iY) + ccphi * s(iY, iY);
 
      // Not in the Karimaki paper, but factors a similar term.
      double se = cosphi * s(iX, iR2) + sinphi * s(iY, iR2);
      double sbb = ccphi * s(iX, iX) + 2. * scphi * s(iX, iY) + ssphi * s(iY, iY);
 
      perigeePrecision(c_Curv, c_Curv) = 0.25 * s(iR2, iR2) - d * (sd - d * (saa + 0.5 * s(iR2) - d * (sa - 0.25 * d * s(iW))));
      perigeePrecision(c_Curv, c_Phi0) = - u * (0.5 * se - d * (sc - 0.5 * d * sb));
      perigeePrecision(c_Phi0, c_Curv) = perigeePrecision(c_Curv, c_Phi0);
      perigeePrecision(c_Phi0, c_Phi0) = u * u * sbb;
 
      perigeePrecision(c_Curv, c_I) = rho * (-0.5 * sd + d * saa) + 0.5 * u * s(iR2) - 0.5 * d * ((2 * u + rho * d) * sa - u * d * s(iW));
      perigeePrecision(c_I, c_Curv) = perigeePrecision(c_Curv, c_I);
      perigeePrecision(c_Phi0, c_I) = u * (rho * sc - u * sb);
      perigeePrecision(c_I, c_Phi0) = perigeePrecision(c_Phi0, c_I);
      perigeePrecision(c_I, c_I) = rho * (rho * saa - 2 * u * sa) + u * u * s(iW);
    }
    return perigeePrecision;
  }
}
 
 
 
UncertainPerigeeCircle KarimakisMethod::fitInternal(CDCObservations2D& observations2D) const
{
  // Matrix of weighted sums
  Eigen::Matrix< double, 4, 4> sNoL = getWXYRSumMatrix(observations2D);
 
  // Matrix of averages
  Eigen::Matrix<double, 4, 4> aNoL = sNoL / sNoL(iW);
 
  // Measurement means
  Eigen::Matrix<double, 4, 1> meansNoL = aNoL.row(iW);
 
  // Covariance matrix
  Eigen::Matrix<double, 4, 4> cNoL = aNoL - meansNoL * meansNoL.transpose();
 
  // Determine NDF : Circle fit eats up to 3 degrees of freedom debpending on the constraints
  size_t ndf = observations2D.size() - 2;
 
  if (not isLineConstrained()) {
    --ndf;
  }
 
  // Parameters to be fitted
  UncertainPerigeeCircle resultCircle = fitKarimaki(sNoL(iW), meansNoL, cNoL, isLineConstrained());
  double chi2 = calcChi2Karimaki(resultCircle, sNoL(iW), cNoL);
 
  PerigeePrecision perigeePrecision = calcPrecisionKarimaki(resultCircle, sNoL, isLineConstrained());
 
  // Use in pivotingin caset the matrix is not full rank as is for the constrained cases-
  PerigeeCovariance perigeeCovariance = PerigeeUtil::covarianceFromPrecision(perigeePrecision);
 
  resultCircle.setChi2(chi2);
  resultCircle.setNDF(ndf);
  resultCircle.setPerigeeCovariance(perigeeCovariance);
  return resultCircle;
}