The Cosmology API Astropy Compatibility Layer#

cosmology.compat.astropy is a Cosmology API compatibility layer for astropy. With this module, you can use any FLRW-based astropy cosmology in any context that accepts a Cosmology API cosmology.

The two components of this module are:

StandardCosmologyWrapper

The Cosmology API wrapper for FLRW.

constants

Astropy cosmology constants.

Quick Start#

We can write a function that accepts any Cosmology API cosmology…

# No implementation, just a description of the interface!
from cosmology.api import StandardCosmology


def flat_angular_diameter_distance(
    cosmo: StandardCosmology[Array, Array], z: Array
) -> Array:
    # Do some cosmology with any object that implements the API
    if cosmo.Omega_k0 != 0:
        raise ValueError("This function only works for flat cosmologies")
    return cosmo.comoving_distance(z) / (1 + z)

and then use it with any Cosmology API cosmology, specifically cosmology.compat.astropy!

We make a compatible astropy cosmology using this library…

from astropy.cosmology import Planck18 as astropy_planck18
from cosmology.compat.astropy import StandardCosmologyWrapper

planck18 = StandardCosmologyWrapper(astropy_planck18)

import astropy.units as u
import astropy.cosmology.units as cu

z = u.Quantity([0.1, 0.2, 0.3], cu.redshift)

which now works with the above function.

>>> flat_angular_diameter_distance(planck18, z)
<Quantity [393.2415434 , 702.98158286, 948.2358979 ] Mpc>

Contributors#

Main authors: Nathaniel Starkman, Nicolas Tessore

All contributors (alphabetical last name):