UnitsManager

class PlasmaCalcs.units.units_manager.UnitsManager(units='si', *, M=1, l=1, t=1, q=1, K=1, sic_quantities=None)

Bases: object

Manages units, including conversion factors and physical constants in different unit systems.

Parameters:

units – str the default unit system to convert to (“si”, “raw”, or “cgs”)
M – value, default 1. Mass_si = M * Mass_raw
l – value, default 1. Length_si = l * Length_raw
t – value, default 1. Time_si = t * Time_raw
q – value, default 1. Charge_si = q * Charge_raw
K – value, default 1. Temperature_si = K * Temperature_raw
sic_quantities – iterable calculate all these conversion factors & shorthands once, ahead of time. if None, use cls.SIC_QUANTITIES (default empty list)

To alter cgs unit conversions (e.g. to specify q units), make a new self.CGS_UNITS.

The default is CGS_UNITS = UnitsManager(M=1e-3, l=1e2, t=1, q=None, K=1). (don’t alter the default one directly; make a new one with the desired values.) q=None is the default because electromagnetic cgs units are ambiguous,

there are multiple options for how to convert to si and the equations differ.

— UnitsManager.help() will print a helpful message: —

BASES tells all the SI base unit symbols. KNOWN tells all the known conversions between symbols (just strings, not numerical values). PHYSICAL_CONSTANTS_SI tells all the known physical constants, as tuples of (SI value, units string)). physical_constants_raw (or pcr) tells all the known physical constants, in ‘raw’ units;

first do self.populate_pcr() to calculate them all.

self.sic tells all the known values for unit conversions, from raw to SI.

e.g., Mass [raw] * self.sic[‘M’] == Mass [si]. new conversion factors are cached here the first time they are calculated,

to avoid recalculating the values multiple times.

to remove all cached values, self.clear_sic().

call the object to get conversion factor. E.g.:

density_si = density_raw * self(‘r’, ‘si’, ‘raw’) density_raw = density_si * self(‘r’, ‘raw’, ‘si’)

or call the object to get physical constant. E.g.:

c_si = self(‘c’, ‘si’) # speed of light in ‘si’ units c_raw = self(‘c’, ‘raw’) # speed of light in ‘raw’ units.

Conversion factors can be combined and raised to powers, e.g.:

self(‘u0.5 m-1’) == self(‘u’)**0.5 * self(‘m’)**-1

Methods

`__call__`(ustr[, units, convert_from, alt])	return quantity or conversion factor in the specified unit system. ustr: str physical constant or quantity (e.g. "c" for speed of light or "M" for mass units) units: UNSET, None, 'si', 'raw', or 'cgs' unit system to convert to. UNSET --> units = self.alts.get(alt, self.units). (Equivalent to None if alt is None) None --> use self.units. convert_from: 'si', 'raw', or 'cgs' unit system to convert from. Ignored if ustr is a quantity (e.g. "c") instead of conversion factor (e.g. "mass") alt: object (probably None or str) if units is UNSET, use units = self.alts.get(alt, self.units) otherwise, alt must be None. :return: a converted physical constant or a conversion factor.
`CGS_UNITS_DEFAULT`()	UnitsManager for cgs units.
`calc_sic_factor`(ustr)	Calculate conversion factor from raw units to SI units.
`clear_sic`()	clear self.sic.
`get_sic_factor`(ustr)	Get conversion factor from raw units to SI units.
`help`()	prints a helpful message about using cls.
`init_sic`()	initialize self.sic from self.bases.
`is_trivial`()	returns whether self has only trivial conversion factors in it (all factors 1 or not provided).
`populate_physical_constants_raw`([quantities])	Calculate all the physical constants in raw units. :param quantities: None or iterable of strings calculate only these physical constants. if None, use self.PHYSICAL_CONSTANTS_SI.keys() :return: self.physical_constants_raw, after creating and filling it.
`populate_sic`([quantities, reset])	Calculate lots of conversion factors. :param quantities: None or iterable of strings calculate these conversion factors and put them in self.sic. e.g. "p", "momentum", "M u", "kg m s-1". if None, use self.SIC_QUANTITIES. :reset: bool, default False. if True, clear self.sic before calculating. :return: self.sic, after adding all the requested conversion factors.
`string_to_si_bases`(string_of_units)	convert string of any units to string of SI base units.
`_base_unit_property`(longname)	create property for base unit -- link to self.bases[ustr].
`_init_from_bases`()	initialize all other parts of self, using self.bases (and self._init_sic_quantities).
`_repr_show_factors`()	returns dict of name and conversion factor to si, to include in repr(self).

Attributes

`BASES`
`CGS_UNITS`	UnitsManager for cgs units.
`K`	Temperature_si = K * Temperature_raw
`KNOWN`
`M`	Mass_si = M * Mass_raw
`PHYSICAL_CONSTANTS_SI`
`SIC_QUANTITIES`
`alts`	dict of {key: units} for alternative objects' unit systems.
`display_precision`
`l`	Length_si = l * Length_raw
`pcr`	alias to physical_constants_raw
`physical_constants_raw`	dict of all the physical constants in raw units.
`q`	Charge_si = q * Charge_raw
`t`	Time_si = t * Time_raw

property CGS_UNITS: UnitsManager for cgs units. Default is UnitsManager(M=1e-3, l=1e2, t=1, q=None, K=1).

q=None is the default because electromagnetic cgs units are ambiguous,

there are multiple options for how to convert to si and the equations differ.

Note that for CGS_UNITS, ‘raw’ means ‘cgs’.

Feel free to set self.CGS_UNITS = a new UnitsManager with a known q,

if you have decided on a specific cgs system to remove relevant ambiguities.

classmethod CGS_UNITS_DEFAULT(): UnitsManager for cgs units. Default is UnitsManager(M=1e-3, l=1e2, t=1, q=None, K=1).

q=None is the default because electromagnetic cgs units are ambiguous,

there are multiple options for how to convert to si and the equations differ.

Note that for the CGS_UNITS result,’raw’ means ‘cgs’.

property K: Temperature_si = K * Temperature_raw

property M: Mass_si = M * Mass_raw

__call__(ustr, units=UNSET, convert_from='raw', *, alt=None)

return quantity or conversion factor in the specified unit system. ustr: str

physical constant or quantity (e.g. “c” for speed of light or “M” for mass units)

units: UNSET, None, ‘si’, ‘raw’, or ‘cgs’: unit system to convert to. UNSET –> units = self.alts.get(alt, self.units). (Equivalent to None if alt is None) None –> use self.units.
convert_from: ‘si’, ‘raw’, or ‘cgs’: unit system to convert from. Ignored if ustr is a quantity (e.g. “c”) instead of conversion factor (e.g. “mass”)
alt: object (probably None or str): if units is UNSET, use units = self.alts.get(alt, self.units) otherwise, alt must be None.

Returns:: a converted physical constant or a conversion factor

_base_unit_property(longname): create property for base unit – link to self.bases[ustr]. re-initialize self if changed.

_init_from_bases(): initialize all other parts of self, using self.bases (and self._init_sic_quantities).

_repr_show_factors(): returns dict of name and conversion factor to si, to include in repr(self).

Here, include l, t, M, and q. Also include K if it is not 1.

property alts: dict of {key: units} for alternative objects’ unit systems.

e.g. CoordsUnitsHaver might set alts[‘coords’] = ‘si’ to indicate coords always in si.

calc_sic_factor(ustr): Calculate conversion factor from raw units to SI units. Also save result in self.sic for future use. :param ustr: string of units (e.g. “m-3”) :return: conversion factor from raw units to SI units

clear_sic(): clear self.sic. delete self.sic, then do self.init_sic()

get_sic_factor(ustr)

Get conversion factor from raw units to SI units. If not already calculated, calculate it first. :param ustr: string of units (e.g. “m-3”) :return: conversion factor from raw units to SI units

if None, raise UnitsUnknownError instead.

classmethod help(): prints a helpful message about using cls.

init_sic(): initialize self.sic from self.bases.

is_trivial(): returns whether self has only trivial conversion factors in it (all factors 1 or not provided).

property l: Length_si = l * Length_raw

property pcr: alias to physical_constants_raw

property physical_constants_raw: dict of all the physical constants in raw units.

populate_physical_constants_raw(quantities=None)

Calculate all the physical constants in raw units. :param quantities: None or iterable of strings

calculate only these physical constants. if None, use self.PHYSICAL_CONSTANTS_SI.keys()

Returns:: self.physical_constants_raw, after creating and filling it.

populate_sic(quantities=None, *, reset=False)

Calculate lots of conversion factors. :param quantities: None or iterable of strings

calculate these conversion factors and put them in self.sic. e.g. “p”, “momentum”, “M u”, “kg m s-1”. if None, use self.SIC_QUANTITIES.

Reset:: bool, default False. if True, clear self.sic before calculating.
Returns:: self.sic, after adding all the requested conversion factors.

property q: Charge_si = q * Charge_raw

string_to_si_bases(string_of_units): convert string of any units to string of SI base units.

property t: Time_si = t * Time_raw