celeritas::units Namespace Reference

Units in Celeritas for macro-scale quantities. More...

Classes
struct	CLight
	Natural unit of speed. More...
struct	EElectron
	Natural unit of charge (positive electron) More...
struct	ElectronVolt
	Atom-scale energy. More...
struct	Mev
	Nucleus-scale energy. More...
struct	MevPerCsq
	Nucleus-scale mass. More...
struct	MevPerC
	Nucleus-scale momentum. More...
struct	Amu
	Atomic mass units [amu]. More...
struct	Barn
	Barn cross section [b]. More...
struct	Millibarn
	Millibarn cross section [mb]. More...
struct	Mol
	Amount of substance \(N_a\). More...
struct	Centimeter
struct	Gram
struct	Gauss
struct	InvCentimeterCubed
	Inverse cubic centimeter for number densities. More...
struct	MolPerCentimeterCubed
	Molar density. More...
struct	GramPerCentimeterCubed
	Mass density. More...
struct	Meter
struct	Kilogram
struct	Second
struct	Tesla
struct	Millimeter
struct	Nanosecond
struct	ClhepUnitMass
	Unit mass in CLHEP system. More...
struct	ClhepUnitBField
	Unit magnetic flux density in CLHEP system. More...
struct	Native
	Mark as being in the native/builtin unit system. More...
struct	LogMev
	Annotate a quantity represented the logarithm of (E/MeV) More...
struct	UnitSystemTraits
	Traits class for units. More...

Typedefs
Quantities for atomic scale/natural units
using	ElementaryCharge = Quantity< EElectron >
using	MevEnergy = Quantity< Mev >
using	LogMevEnergy = Quantity< LogMev >
using	MevMass = Quantity< MevPerCsq >
using	MevMomentum = Quantity< MevPerC >
using	MevMomentumSq = Quantity< UnitProduct< MevPerC, MevPerC > >
using	LightSpeed = Quantity< CLight >
using	AmuMass = Quantity< Amu >
Quantities for manual input and/or test harnesses
using	BarnXs = Quantity< Barn >
using	CmLength = Quantity< Centimeter >
using	InvCmXs = Quantity< UnitInverse< Centimeter > >
using	InvCcDensity = Quantity< InvCentimeterCubed >
using	MolCcDensity = Quantity< MolPerCentimeterCubed >
using	GramCcDensity = Quantity< GramPerCentimeterCubed >
using	FieldTesla = Quantity< Tesla >
Type aliases for unit system traits
using	CgsTraits = UnitSystemTraits< UnitSystem::cgs >
using	SiTraits = UnitSystemTraits< UnitSystem::si >
using	ClhepTraits = UnitSystemTraits< UnitSystem::clhep >
using	NativeTraits = UnitSystemTraits< UnitSystem::native >

Functions
template<class F >
constexpr decltype(auto)	visit_unit_system (F &&func, UnitSystem sys)
	Expand a macro to a switch statement over all possible unit system types. More...

Variables
Units with numerical value defined to be 1 for CGS
constexpr real_type	centimeter = 1
	Length.
constexpr real_type	gram = 1
	Mass.
constexpr real_type	second = 1
	Time.
constexpr real_type	gauss = 1
	Field strength.
constexpr real_type	kelvin = 1
	Temperature.
Exact unit transformations to SI units
constexpr real_type	meter = 100 * centimeter
constexpr real_type	kilogram = 1000 * gram
constexpr real_type	tesla = 10000 * gauss
Exact unit transformations using SI unit definitions
constexpr real_type	newton = kilogram * meter / (second * second)
constexpr real_type	joule = newton * meter
constexpr real_type	coulomb = kilogram / (tesla * second)
constexpr real_type	ampere = coulomb / second
constexpr real_type	volt = joule / coulomb
constexpr real_type	farad = coulomb / volt
CLHEP units
constexpr real_type	millimeter = real_type(0.1) * centimeter
constexpr real_type	nanosecond = real_type(1e-9) * second
Other common units
constexpr real_type	micrometer = real_type(1e-4) * centimeter
constexpr real_type	nanometer = real_type(1e-7) * centimeter
constexpr real_type	femtometer = real_type(1e-13) * centimeter
constexpr real_type	barn = real_type(1e-24) * centimeter * centimeter

Detailed Description

Units in Celeritas for macro-scale quantities.

Celeritas can be configured at build time to use different unit systems for better compatibility with external libraries and applications. The CELERITAS_UNITS CMake variable can be set to one of the following:

• CELERITAS_UNITS_CGS (default): use Gaussian CGS units
• CELERITAS_UNITS_SI: use SI units
• CELERITAS_UNITS_CLHEP: use the Geant4 high energy physics system (a mix of macro-scale and atomic-scale units)

The following units have numerical values of 1 in the default Celeritas system (Gaussian CGS) and are often seen in unit tests:

• cm for standard unit of length
• s for standard unit of time
• g for standard unit of mass
• G for standard unit of field strength

Unless otherwise specified, this unit system is used for input and output numerical values. They are meant for macro-scale quantities coupling the different code components of Celeritas.

Note

This system of units should be fully consistent so that constants can be precisely defined. (E.g., you cannot define both MeV as 1 and Joule as 1.) To express quantities in another system of units, such as MeV and "natural" units, use the Quantity class.

See also:

• Constants.hh for constants defined in this unit system
• physics/base/Units.hh for unit systems used by the physics

Additionally:

• radians are used for measures of angle (unitless)

• steradians are used for measures of solid angle (unitless)

  Todo:

  If we're serious about supporting single-precision arithmetic, we should define a helper class that stores the constant as full precision but when multiplied by a single/double is truncated to that precision. Otherwise, if real_type is single-precision, then we lose accuracy in places like the GeantImporter where everything is double precision.

Function Documentation

visit_unit_system()

template<class F >

constexpr decltype(auto) celeritas::units::visit_unit_system ( F &&  func, UnitSystem  sys  )

constexpr

Expand a macro to a switch statement over all possible unit system types.

This helper function is meant for processing user input to convert values to the native unit system. It is not a CELER_FUNCTION because unit conversion should be done only during preprocessing on the CPU.