NatPy

Convert the units of particle physics quantities

Packages needed:

• astropy
• numpy
• sympy

Basic Usage

Code levarages astropy.units.core.Unit and astropy.units.quantity.Quantity objects.

1. Run import numpy and from astropy import units as u.
2. Run import natpy.
3. Access physical constants with symbol:

>>> natpy.c
<Quantity 2.99792458e+08 m / s>

>>> natpy.hbar
<Quantity 1.05457182e-34 J s>

4. Specify base of natural units with natpy.set_active_units(). Pass a string corresponding to a list of default natural units, or a list of physical constants to set your own. List of default bases found in natpy/default_values.py. (will markdown later)

5. Run natpy.convert() to convert between units, including necessary factors of natural units. Pass just unit objects to obtain conversion factors. Pass quantity objects to perform conversions. E.g.

# kg to keV
>>> natpy.convert(u.kg, u.keV)
5.6173581670146864e+32

# Electron mass
>>> me = natpy.convert(9.11e-31 * u.kg, u.keV)
>>> me
<Quantity 511.74132902 keV>

# Energy of electron with momentum of 1 MeV 
>>> p = 1 * u.MeV
>>> E = np.sqrt(p**2 + me**2)

# Convert to SI units
>>> natpy.convert(E,u.J)
<Quantity 1.79926309e-13 J>

Note: Summing quanties requires conventionally equivalent units.

6. See tests/convert_test.py for more examples.