Package etomica.units

Defines units and dimensions that are used for conversions during input or output. All quantities used internally by the simulation are given in "simulation units", which is based on the Angstrom as the unit of length, the Dalton as the unit of mass, and the picosecond as the unit of time (a Dalton, or atomic mass unit (amu), is one gram divided by Avogadro's number). The classes given in this package can be used to convert between these units and another unit that might be more natural or convenient. The two key elements of the package are the Unit interface and the abstract Dimension class.

Dimension

Instances of Dimension can be used to indicate the physical nature of a value, e.g., whether it is a quantity of mass, length, force, etc. There are two places where this information is routinely provided:

• the package etomica.data defines a Data class which holds a DataInfo instance describing the Data; part of the information given in DataInfo is a Dimension instance which specifies the physical dimensions of the data.
• the convention of defining set/get methods to access and change fields of an object is supplemented with an annotation on the get method specifying the dimension of the value. For example, a class that defines setSize and getSize methods to access the field size (which represents, say, the diameter of a sphere) will also have an annotation on getSize indicating dimensions of length.

Dimensions are specified via a signature, which is an array of seven values indicating the exponents of the fundamental dimensions that are combined to form the specified dimension. The fundamental dimensions follow the convention defined by the SI system, and are

• length
• mass
• time
• electric current
• temperature
• number (of molecules)
• luminous intensity

So, for example, the signature of the energy dimension is length²-mass/time² and is given by the signature array (2, 1, -2, 0, 0, 0, 0). The signature of energy/molecules (e.g., Joules/mole) is (2, 1, -2, 0, 0, -1, 0).

Dimension subclasses are defined for the fundamental dimensions and commonly encountered derived dimensions. These classes have names such as Length, Time, Volume, Energy, and so on. These classes all define static singleton instances with the field name DIMENSION; the field SIM_UNIT in each class gives an instance of Unit that corresponds to the unit derived from simulation units for that dimension. Other dimensions can be defined by constructing instances of CompoundDimension.

Unit

Implementations of the Unit interface provide a convenient means to convert between simulation units and some other particular unit, which need be done only when data is read, written, or displayed.

SimpleUnit is a basic class that holds a conversion factor, a Dimension instance and other descriptive information for implementing a basic Unit. Many specific units are defined by extending this class; examples include Kelvin, Bar, Joule, etc.

A PrefixedUnit class takes a Unit instance and a Prefix, which can be used to construct units such as kilograms (combining Prefix.KILO with Gram.UNIT).

Derived units that are not already defined can be constructed using the CompoundUnit class.

The package etomica.units.systems defines constructs that can collect the units defined by conventional unit systems, such as SI, cgs, English, etc.

Interface Summary

Interface	Description
Unit	Interface used to specify the physical units to be used when inputting or outputting a quantity.

Class Summary

Class	Description
Ampere	The ampere unit of electrical current.
Angstrom
Bar	The bar unit of pressure, equal to 10^5 N/m^2.
Barye	The barye unit of pressure, equal to 1 dyn/cm^2.
BohrRadius	The Borh Radius unit of length, corresponding to the size of a Hydrogen atom's electron cloud.
Calorie	The Joule unit of energy, equal to 1 N-m or 1 kg-m^2/s^2.
Candela	The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
CompoundUnit	Unit formed from other units raised to specified powers.
Coulomb	The Coulomb unit of electrical charge.
Count	Unit class for the number, or quantity, of something.
CubicCentimeter	The cubic centimeter unit of volume, cm^3.
CubicMeter	The cubic meter unit of volume, m^3.
Dalton
Debye	The debye unit of electrical dipole moment, equal to 10^-18 statC-cm, or 3.33564e-30 C-m.
Decimal	Decimal representation of something that represents the fractional amount of a whole (e.g., mole fraction) as a decimal value typically between 0 and 1.
Degree	Standard degree angular unit, such that for example a right angle is 90 degrees.
Dyne	The dyne unit of force, equal to 1 g-cm/s^2.
Electron	Unit of charge equal to the magnitude of the charge on an electron.
ElectronVolt	The electronVolt unit of energy, equal to approximately 1.602e-19 Joules.
Erg	The erg unit of energy, equal to 1 dyn-cm or 1 g-cm^2/s^2.
Gram
Hartree
Hertz	The Hertz unit of frequency, equal to 1/second.
Joule	The Joule unit of energy, equal to 1 N-m or 1 kg-m^2/s^2.
Kelvin
Liter	The liter unit of volume, equal to 1000 cm^3 or 0.001 m^3 or 10^27 A^3.
Meter	The meter unit of length, equal to 10^10 angstroms.
Mole	The mole unit of quantity, approximately equal to 6.022e23 simulation units.
Newton	The Newton unit of force, equal to 1 kg-m/s^2.
Pascal	The Pascal unit of pressure, equal to 1 N/m^2.
Percent	Decimal representation of something that represents the fractional amount of a whole (e.g., mole fraction) as a percentage value typically between 0 and 100.
Picosecond	Simulation unit of time.
Pixel	Unit converting between simulation unit of length and pixels rendered in an image.
Poise	The Poise unit of viscosity, equal to 1 gram/(cm-sec).
PrefixedUnit	Implementation of the Unit interface formed from a base Unit (e.
Radian	Simulation unit for the measure of an angle.
Second
SimpleUnit	Superclass for all base unit classes.
Statcoulomb	The statcoulomb unit of electrical charge, which is the standard unit of charge in the CGS unit system.
UnitRatio	Class for constructing units forms as ratios of other units.
Volt	The Volt unit of electric potential.
Watt	The Watt unit of power, equal to 1 J/s or 1 kg-m^2/s^3.

Enum Summary

Enum	Description
Prefix	Base class for all unit prefixes, such as kilo, micro, nano, etc.