PlasmaCalcs.mhd.mhd_units.MhdUnitsManager

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

Bases: UnitsManager

units manager with the from_mhd method,

which determines all units based on u_l, u_t, u_r, and mu0_raw.

Note: cgs units for electromagnetic quantities are not supported here,: because cgs electromagnetic equations differ from SI equations,

e.g. cgs includes extra factors of 4*pi or c in various places.

How to infer electromagnetic units from t, l, r, and mu0?

Internally, this method determines:

u_M = u_r * u_l**3 # mass

u_N = u_M * u_l * u_t**-2 # energy (Newtons in SI)

Amperes units:

(mu0 [si]) = u_N * u_A**-2 * (mu0 [raw])
–> u_A = sqrt(u_N * (mu0 [raw]) / (mu0 [si]))
where mu0 [si] == DEFAULTS.PHYSICAL.CONSTANTS_SI[‘mu0’], approx. 4 * pi * 1e-7.

Which yields, for charge units:

u_q = u_A * u_t

At which point, we have u_l, u_t, u_M, and u_q,

which is sufficient to infer all other units (aside from K for temperature)

— MhdUnitsManager.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

__init__(units='si', *, M=1, l=1, t=1, q=1, K=1, sic_quantities=None)

Methods

`CGS_UNITS_DEFAULT`()
`__init__`([units, M, l, t, q, K, sic_quantities])
`calc_sic_factor`(ustr)	Calculate conversion factor from raw units to SI units.
`clear_sic`()
`from_mhd`([units, mu0_raw, K])
`from_mhd_cgs`([units, mu0_raw, K])
`get_sic_factor`(ustr)	Get conversion factor from raw units to SI units.
`help`()
`init_sic`()
`is_trivial`()
`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)

Attributes

`BASES`
`CGS_UNITS`
`K`
`KNOWN`
`M`
`PHYSICAL_CONSTANTS_SI`
`SIC_QUANTITIES`
`alts`
`display_precision`
`l`
`pcr`
`physical_constants_raw`
`q`
`t`

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

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()

classmethod from_mhd(units='si', *, u_l, u_t, u_r, mu0_raw=1, K=1)

create a MhdUnitsManager from u_l, u_t and u_r, the SI conversion factors.

CAUTION: these are the SI conversion factors. NOT cgs. | (some MHD simulations, like Bifrost, use similar names for the CGS factors.)

units: ‘si’ or ‘raw’: by default, outputs of the resulting UnitsManager convert to this unit system.

Can easily change later by setting result.units to a different value.
u_l: number: length [si] = u_l * length [raw]
u_t: number: time [si] = u_l * time [raw]
u_r: number: mass density [si] = u_r * mass density [raw]
mu0_raw: number, default 1: value of mu0 in ‘raw’ units system. Used to infer Amperes units via:

u_M = u_r * u_l**3 # mass

u_N = u_M * u_l * u_t**-2 # energy (Newtons in SI)

mu0_si = u_N * u_A**-2 * mu0_raw

u_A = sqrt(u_N * mu0_raw / mu0_si)

where mu0_si == DEFAULTS.PHYSICAL.CONSTANTS_SI[‘mu0’], approx. 4 * pi * 1e-7.
K: number, default 1: temperature [si] = K * temperature [raw]

classmethod from_mhd_cgs(units='si', *, ucgs_l, ucgs_t, ucgs_r, mu0_raw=1, K=1)

create a BifrostUnitsManager from ucgs_l, ucgs_t and ucgs_r, the CGS conversion factors.

units: ‘si’ or ‘raw’: by default, outputs of the resulting UnitsManager convert to this unit system.

Can easily change later by setting result.units to a different value.
ucgs_l: number: length [cgs] = ucgs_l * length [raw]
ucgs_t: number: time [cgs] = ucgs_t * time [raw]
ucgs_r: number: mass density [cgs] = ucgs_r * mass density [raw]
mu0_raw: number, default 1: value of mu0 in ‘raw’ units system. Used to infer Amperes units via:

u_M = u_r * u_l**3 # mass

u_N = u_M * u_l * u_t**-2 # energy (Newtons in SI)

mu0_si = u_N * u_A**-2 * mu0_raw

u_A = sqrt(u_N * mu0_raw / mu0_si)

where mu0_si == DEFAULTS.PHYSICAL.CONSTANTS_SI[‘mu0’], approx. 4 * pi * 1e-7.
K: number, default 1: temperature [cgs] = K * temperature [raw]

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