pystein.constants module

Useful Physical Constants

Since the Astropy library provides a wonderful list of predefined constants, the approach here is to extend those objects to behave like sympy symbols. This prevents duplicate definitions of physical constants while providing a natural handle for each value when constructing a symbolic expression using sympy.

We have also extended the Units definition to include natural (Planck) units in which the physical constants c = G = hbar = kB = 1. These units are a geometrized system ideal for general relativity (the focus of this package).

References

[1] NIST CODATA2018 Value of Planck Length https://physics.nist.gov/cgi-bin/cuu/Value?plkl [2] NIST CODATA2018 Value of Planck Mass https://physics.nist.gov/cgi-bin/cuu/Value?plkm [3] NIST CODATA2018 Value of Planck Time https://physics.nist.gov/cgi-bin/cuu/Value?plkt [4] NIST CODATA2018 Value of Planck Temperatur https://physics.nist.gov/cgi-bin/cuu/Value?plktmp

class pystein.constants.ConstantSymbol(constant: astropy.constants.constant.Constant, is_natural_unit: bool = False)

Bases: sympy.core.symbol.Symbol

Constant Symbol is a symbolic representation of a known physical constant, as defined in the astropy.constants module.

property cgs: Pass-thru accessor to constant value in CGS units

property constant: Safe attr access for _constant

default_assumptions = {}

is_constant(): Override this method to instantly return True

property is_natural_unit: Safe attr access for _is_natural_unit

name

property natural: Pass-thru accessor to constant value in Natural units

property si: Pass-thru accessor to constant value in SI units

property unit: Safe attr access for constant.unit

class pystein.constants.UnitSystem(value)

Bases: str, enum.Enum

Unit Systems Constants

CGS = 'cgs'

NATURAL = 'natural'

SI = 'si'

pystein.constants.subs_cgs(expr: sympy.core.expr.Expr) → sympy.core.expr.Expr

Substitute any ConstantSymbols in an Expression with their value in a CGS units

Parameters: expr – Expr, the sympy expression in which to substitute constant symbols for values
Returns: Expr, the substituted expression

pystein.constants.subs_natural(expr: sympy.core.expr.Expr) → sympy.core.expr.Expr

Substitute any ConstantSymbols in an Expression with their value in a NATURAL units

Parameters: expr – Expr, the sympy expression in which to substitute constant symbols for values
Returns: Expr, the substituted expression

pystein.constants.subs_si(expr: sympy.core.expr.Expr) → sympy.core.expr.Expr

Substitute any ConstantSymbols in an Expression with their value in a SI units

Parameters: expr – Expr, the sympy expression in which to substitute constant symbols for values
Returns: Expr, the substituted expression