Units.hpp

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#pragma once
 
#include <mp-units/systems/hep.h>  // exports framework.h; includes systems/si.h
 
#include <array>
 
namespace ship {
 
namespace units {
 
// Length
inline constexpr auto mm = mp_units::si::milli<mp_units::si::metre>;
inline constexpr auto cm = mp_units::si::centi<mp_units::si::metre>;
inline constexpr auto m = mp_units::si::metre;
 
// Time
inline constexpr auto ns = mp_units::si::nano<mp_units::si::second>;
inline constexpr auto s = mp_units::si::second;
 
// Angle
inline constexpr auto rad = mp_units::si::radian;
 
// Energy
inline constexpr auto MeV = mp_units::hep::unit_symbols::MeV;
inline constexpr auto GeV = mp_units::hep::unit_symbols::GeV;
 
// Speed of light as a named unit ("c", exact by SI definition). Building
// momentum, mass and time-of-flight units from it keeps every conversion
// factor derived rather than hand-typed.
inline constexpr auto c = mp_units::hep::speed_of_light;
 
// Momentum and mass
inline constexpr auto GeV_per_c = GeV / c;
inline constexpr auto GeV_per_c2 = GeV / mp_units::square(c);
 
// Time of flight per unit length (Pythia8 production time, lifetime cuts)
inline constexpr auto mm_per_c = mm / c;
 
// Magnetic flux density
inline constexpr auto tesla = mp_units::si::tesla;
 
}  // namespace units
 
using Length = mp_units::quantity<units::mm, double>;
using Time = mp_units::quantity<units::ns, double>;
using Energy = mp_units::quantity<units::GeV, double>;
using Momentum = mp_units::quantity<units::GeV_per_c, double>;
using Mass = mp_units::quantity<units::GeV_per_c2, double>;
using Angle = mp_units::quantity<units::rad, double>;
using MagneticField = mp_units::quantity<units::tesla, double>;
 
template <typename Q>
using Vec3 = std::array<Q, 3>;
 
template <typename Q>
[[nodiscard]] constexpr Q quantityOf(double v) {
  return v * Q::reference;
}
 
template <typename Q>
[[nodiscard]] constexpr double raw(Q q) {
  return q.numerical_value_in(Q::unit);
}
 
template <typename Q>
[[nodiscard]] constexpr Vec3<Q> vecOf(std::array<double, 3> const& v) {
  return {v[0] * Q::reference, v[1] * Q::reference, v[2] * Q::reference};
}
 
template <typename Q>
[[nodiscard]] constexpr std::array<double, 3> raw(Vec3<Q> const& v) {
  return {v[0].numerical_value_in(Q::unit), v[1].numerical_value_in(Q::unit),
          v[2].numerical_value_in(Q::unit)};
}
 
}  // namespace ship