"""
=========================================
Physical constants (:mod:`sisl.constant`)
=========================================
.. module:: sisl.constant
Module containing a pre-set set of physical constants. The SI units are following the *new* convention
that takes effect on 20 May 2019.
The currently stored constants are (all are given in SI units):
.. autosummary::
PhysicalConstant
q
c
h
hbar
m_e
m_p
G0
G
.. we need to add them to the toctree to be able to create links to them
.. autosummary::
:toctree:
:hidden:
PhysicalConstant
q
c
h
hbar
m_e
m_p
G0
G
All constants may be used like an ordinary float (which converts it to a float:
>>> c
299792458.0 m/s
>>> c * 2
599584916
while one can just as easily convert the units (which ensures thay stay like another `PhysicalConstant`):
>>> c('Ang/ps')
2997924.58 Ang/ps
"""
from __future__ import print_function, division
from sisl.unit.base import units
__all__ = ['PhysicalConstant']
[docs]class PhysicalConstant(float):
""" Class to create a physical constant with unit-conversion capability, works exactly like a float.
To change the units simply call it like a method with the desired unit:
>>> m = PhysicalConstant(1., 'm')
>>> m.unit
'm'
>>> m2nm = m('nm')
>>> m2nm
1000000000.0 nm
>>> m2nm.unit
'nm'
>>> m2nm * 2
1000000000.0
"""
__slots__ = ['_unit']
def __new__(cls, value, unit):
c = float.__new__(cls, value)
c._unit = unit
return c
@property
def unit(self):
""" Unit of constant """
return self._unit
def __str__(self):
return '{} {}'.format(float(self), self.unit)
def __call__(self, unit=None):
""" Return the value for the constant in the given unit, otherwise will return the units in SI units """
if unit is None:
return self
return PhysicalConstant(self * units(self.unit, unit), unit)
__all__ += ['q', 'c', 'h', 'hbar', 'm_e', 'm_p', 'G', 'G0']
#: Unit of charge [C], or [A s]
q = PhysicalConstant(1.602176634e-19, 'A s')
#: Speed of light [m/s]
c = PhysicalConstant(299792458, 'm/s')
#: Plancks constant [J s]
h = PhysicalConstant(6.62607015e-34, 'J s')
#: Reduced Plancks constant [J s]
hbar = PhysicalConstant(1.0545718176461565e-34, 'J s')
#: Mass of electron [kg]
m_e = PhysicalConstant(9.1093835611e-31, 'kg')
#: Mass of proton [kg]
m_p = PhysicalConstant(1.67262189821e-27, 'kg')
#: Conductance quantum [S], or [m^2/s^2]
G0 = PhysicalConstant(2 * (q ** 2 / h), 'm^2/s^2')
#: Gravitational constant [m^3/kg/s^2]
G = PhysicalConstant(6.6740831e-11, 'm^3/kg/s^2')