CylindricalState.h

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#ifndef CylindricalState_H
#define CylindricalState_H

#include "DataFormats/GeometryVector/interface/LocalPoint.h"
#include "DataFormats/GeometryVector/interface/LocalVector.h"
#include "FWCore/Utilities/interface/Visibility.h"
#include "RKSmallVector.h"

#include <iostream>

class dso_internal CylindricalState {
public:
  typedef double Scalar;
  typedef RKSmallVector<Scalar, 5> Vector;

  CylindricalState() {}

  CylindricalState(const LocalPoint& pos, const LocalVector& mom, Scalar ch) {
    rho_ = pos.perp();
    Scalar cosphi = pos.x() / rho_;
    Scalar sinphi = pos.y() / rho_;
    Scalar p_rho = mom.x() * cosphi + mom.y() * sinphi;
    Scalar p_phi = -mom.x() * sinphi + mom.y() * cosphi;

    par_(0) = pos.phi();
    par_(1) = pos.z();
    par_(2) = p_phi / (p_rho * rho_);
    par_(3) = mom.z() / p_rho;
    par_(4) = ch / mom.mag();

    prSign_ = p_rho > 0 ? 1.0 : -1.0;

    std::cout << "CylindricalState built from pos " << pos << " mom " << mom << " charge " << ch << std::endl;
    std::cout << "p_rho " << p_rho << " p_phi " << p_phi << " dphi_drho " << par_(2) << std::endl;
    std::cout << "Which results in                " << position() << " mom " << momentum() << " charge " << charge()
              << std::endl;
  }

  CylindricalState(Scalar rho, const Vector& par, Scalar prSign) : par_(par), rho_(rho), prSign_(prSign) {}

  const LocalPoint position() const { return LocalPoint(LocalPoint::Cylindrical(rho_, par_(0), par_(1))); }

  const LocalVector momentum() const {
    Scalar cosphi = cos(par_(0));
    Scalar sinphi = sin(par_(0));
    Scalar Q = sqrt(1 + rho_ * rho_ * par_(2) * par_(2) + par_(3) * par_(3));
    Scalar P = std::abs(1. / par_(4));
    Scalar p_rho = prSign_ * P / Q;
    Scalar p_phi = rho_ * par_(2) * p_rho;
    Scalar p_z = par_(3) * p_rho;
    LocalVector result(p_rho * cosphi - p_phi * sinphi, p_rho * sinphi + p_phi * cosphi, p_z);
    return result;
  }

  const Vector& parameters() const { return par_; }

  Scalar charge() const { return par_(4) > 0 ? 1 : -1; }

  Scalar rho() const { return rho_; }

  double prSign() const { return prSign_; }

private:
  Vector par_;
  Scalar rho_;
  Scalar prSign_;  
};

#endif