Used to indicate an object of that type or that can instantiate that type. For example, "He 2+" is particle-like because it can be used to instantiate Particle.


An abbreviated version of a commonly used function. For example, va_ is an alias for Alfven_speed. Aliases are named with a trailing underscore.

For further details, please refer to the contributor guide’s section on aliases.


An abbreviation for positional arguments.


A particle-like object is atom-like if it is or could be cast into:

  • A Particle representing an element, isotope, or ionic level; or

  • A ParticleList including only elements, isotopes, or ionic levels.

For example, "p+", "He-4", "deuterium", "O 0+", Particle("Fe-56 16+)", ["He-4 1+", "He-4 2+"], and integers representing atomic numbers are all atom-like.

Examples of objects that are particle-like but not atom-like include "neutron", "e-", and ["e-", "e+"]. Additionally, ["He-4", "e-"] is not atom-like because this list contains an item that is not atom-like.

Please refer to the glossary entry for particle-like for a full description of valid representations of elements, isotopes, and ions.

charge number

The electrical charge of a particle in units of the elementary charge. The charge number of an ion or neutral particle is usually denoted as Z.


Any instance of a subclass of AbstractFitFunction. Also see module fit_functions.

integration test

An integration test verifies that multiple software components work together as intended.

Compared to a unit test, an integration test is typically harder to write, slower to run, more difficult to maintain, and less useful at pinpointing the specific cause of a problem. However, integration tests are able to find problems that unit tests cannot. In particular, integration tests are able to find problems at the interfaces between different modules. On average, each integration test covers more lines of code than each related unit test. Because unit tests and integration tests complement each other, both are important constituents of a test suite.


An argument or parameter is keyword-only when the argument must be provided with the name of the corresponding parameter.

If z is a keyword-only parameter to f(z), then the argument 2 can be provided as f(z=2) but not f(2).


An abbreviation for keyword arguments.


An optimized version of an existing plasmapy function intended for applications where computational efficiency is most important. While most formulary functions accept Quantity objects created using astropy.units, lite-functions accept numbers and array_like inputs that are implicitly assumed to be in SI units. The name of a lite-function ends with _lite. A lite-function can be accessed as the lite attribute of the corresponding regular function.


Unlike most formulary functions, no validations are performed on the arguments provided to a lite-function for the sake of computational efficiency. When using lite-functions, it is vital to double-check your implementation!

For further details, please refer to the contributor guide’s section on lite-functions.


An object is particle-like if it is a Particle or CustomParticle, or can be cast into one.

An element may be represented by a string containing the atomic symbol (case-sensitive), the name of the element, or an integer representing the atomic number. The element iron can be represented as "Fe", "iron", or 26.

An isotope may be represented by a string that contains an atomic symbol or element name, followed by a hyphen and the mass number (with no spaces in between). The isotope 56Fe can be represented as "Fe-56", or "iron-56". 2H can be represented by "D" or "deuterium", and 3H can be represented by "T" or "tritium".

An ion or neutral atom may be represented by a string that contains a representation of an element or isotope, followed by charge information which is typically an integer representing the charge number and a plus or minus sign to indicate the electrical charge. For example, a deuteron may be represented as "D 1+" and 56Fe1+ may be represented as "Fe-56 1+".

A special particle may be represented by a string that contains the name of the particle (case insensitive) or a standard symbol for it (case insensitive). A neutron can be represented as "n" or "neutron"; a proton can be represented as "p+", "p", or "proton"; and an electron can be represented by "e-", "e", or "electron".

DimensionlessParticle instances are not particle-like because, without normalization information, they do not uniquely identify a physical particle.

For more complete details, refer to ParticleLike.


An object is particle-list-like if it is a ParticleList, or can be cast into one.

For more complete details, refer to ParticleListLike.

real number

Any numeric type that represents a real number. This could include a float, int, a dimensionless Quantity, or any of the numpy.number types. Note that if a PlasmaPy function expects a dimensional Quantity and a real number is provided, then the real number is often assumed to have the appropriate SI units.


Most functions in PlasmaPy accept temperature, \(T\), as a Quantity with units of temperature (e.g., kelvin) or energy (e.g., electron-volts). A value for energy that is provided will be divided by the Boltzmann constant, \(k_B\), to be converted into units of temperature.

unit test

A unit test verifies a single unit of behavior, does it quickly, and does it in isolation from other tests [Khorikov, 2020].

Unit tests are intended to provide fast feedback that help pinpoint the locations of errors. Unit tests often abide by the following pattern [Osherove, 2013]:

  1. Arrange: gather inputs and get the system to the state in which the test is expected to run.

  2. Act: make the system under test undertake the operation that is being tested.

  3. Assert: verify that the actual outcome of the act phase matches the expected outcome.

In a unit test for a function, the arrange phase involves collecting or constructing the inputs for the function. The act phase occurs when the function is called with those inputs. The assert phase is when the value returned by the function is compared to the expected result.