NatPy

Convert the units of particle physics quantities

Packages needed:

• astropy
• numpy

Guided Tutorial

https://github.com/AndreScaffidi/Natpy_pyhep_2021

Basic Usage

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

1. Run import natpy.

2. Access physical constants with symbol within const:

   >>> import natpy as nat
   
   >>> nat.const.c
   <class 'astropy.constants.codata2018.CODATA2018'> name='Speed of light in vacuum' value=299792458.0 uncertainty=0.0 unit='m / s' reference='CODATA 2018'>
   
   
   >>> nat.const.hbar
   <class 'astropy.constants.codata2018.CODATA2018'> name='Reduced Planck constant' value=1.0545718176461565e-34 uncertainty=0.0 unit='J s' reference='CODATA 2018'>
   
   

3. Access units with symbol. Combine with values or numpy objects to form quantities:

   >>> nat.m
   Unit("m")
   
   >>> nat.m / nat.s
   Unit("m / s")
   
   >>> 500 * nat.MeV
   <Quantity 500. MeV>
   

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. The list of default bases may be found in natpy/default_values.py. The default sets c = ℏ = ε₀ = 1.

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.

   >>> import natpy as nat
   
   # kg to keV
   >>> nat.convert(nat.kg, nat.keV)
   5.6173581670146864e+32
   
   # Electron mass
   >>> me = nat.convert(9.11e-31 * nat.kg, nat.keV)
   >>> me
   <Quantity 511.74132902 keV>
   
   # Energy of electron with momentum of 1 MeV
   >>> p = 1 * nat.MeV
   >>> E = np.sqrt(p**2 + me**2)
   
   # Convert to SI units
   >>> nat.convert(E, nat.J)
   <Quantity 1.79926309e-13 J>
   

   Note: Summing quantities of compatible units results in a quantity with the first terms units.

6. natpy.convert() may also be accessed as a method for unit or quantity objects.

   >>> import natpy as nat
   
   >>> nat.GeV.convert( nat.fm**(-1) )
   5.067730716156395
   
   >>> (1 * nat.GeV).convert( nat.fm**(-1) )
   <Quantity 5.06773072 1 / fm>
   

7. Electromagnetic constants are defined in the SI system by default:

   >>> nat.const.e
   <<class 'astropy.constants.codata2018.EMCODATA2018'> name='Electron charge' value=1.602176634e-19 uncertainty=0.0 unit='C' reference='CODATA 2018'>
   

   Values may be accessed in other systems as attributes of the nat.const.cgs submodule:

   >>> nat.const.cgs.e.gauss
   <<class 'astropy.constants.codata2018.EMCODATA2018'> name='Electron charge' value=4.803204712570263e-10 uncertainty=0.0 unit='Fr' reference='CODATA 2018'>
   

   The default system may be changed using natpy.set_active_em_system(), with arguments si, gauss, esu or emu:

   >>> nat.set_active_em_system('gauss')
   >>> nat.const.e
   <<class 'astropy.constants.codata2018.EMCODATA2018'> name='Electron charge' value=4.803204712570263e-10 uncertainty=0.0 unit='Fr' reference='CODATA 2018'>
   

8. Dimensionless unscales quantities may be constructed using natpy.dimensionless_unscaled, which is also bound to natpy.dimensionless, natpy.unitless and natpy.one, for added usability.

9. See examples/conversion.py for more examples.