astropy.cosmology.cosmology_equal(cosmo1: Any, cosmo2: Any, /, *, allow_equivalent: bool = False) bool[source]#

Return element-wise equality check on the cosmologies.


Cosmologies are currently scalar in their parameters.

cosmo1, cosmo2Cosmology-like

The objects to compare. Must be convertible to Cosmology, as specified by format.

formatbool or None or str or tuple thereof, optional keyword-only

Whether to allow the arguments to be converted to a Cosmology. This allows, e.g. a Table to be given instead a Cosmology. False (default) will not allow conversion. True or None will, and will use the auto-identification to try to infer the correct format. A str is assumed to be the correct format to use when converting. Note format is broadcast as an object array to match the shape of cosmos so format cannot determine the output shape.

allow_equivalentbool, optional keyword-only

Whether to allow cosmologies to be equal even if not of the same class. For example, an instance of LambdaCDM might have \(\Omega_0=1\) and \(\Omega_k=0\) and therefore be flat, like FlatLambdaCDM.


Assuming the following imports

>>> import astropy.units as u
>>> from astropy.cosmology import FlatLambdaCDM

Two identical cosmologies are equal.

>>> cosmo1 = FlatLambdaCDM(70 * (, 0.3)
>>> cosmo2 = FlatLambdaCDM(70 * (, 0.3)
>>> cosmology_equal(cosmo1, cosmo2)

And cosmologies with different parameters are not.

>>> cosmo3 = FlatLambdaCDM(70 * (, 0.4)
>>> cosmology_equal(cosmo1, cosmo3)

Two cosmologies may be equivalent even if not of the same class. In these examples the LambdaCDM has Ode0 set to the same value calculated in FlatLambdaCDM.

>>> from astropy.cosmology import LambdaCDM
>>> cosmo3 = LambdaCDM(70 * (, 0.3, 0.7)
>>> cosmology_equal(cosmo1, cosmo3)
>>> cosmology_equal(cosmo1, cosmo3, allow_equivalent=True)

While in this example, the cosmologies are not equivalent.

>>> cosmo4 = FlatLambdaCDM(70 * (, 0.3, Tcmb0=3 * u.K)
>>> cosmology_equal(cosmo3, cosmo4, allow_equivalent=True)

Also, using the keyword argument, the notion of equality is extended to any Python object that can be converted to a Cosmology.

>>> mapping = cosmo2.to_format("mapping")
>>> cosmology_equal(cosmo1, mapping, format=True)

Either (or both) arguments can be Cosmology-like.

>>> cosmology_equal(mapping, cosmo2, format=True)

The list of valid formats, e.g. the Table in this example, may be checked with Cosmology.from_format.list_formats().

As can be seen in the list of formats, not all formats can be auto-identified by Cosmology.from_format.registry. Objects of these kinds can still be checked for equality, but the correct format string must be used.

>>> yml = cosmo2.to_format("yaml")
>>> cosmology_equal(cosmo1, yml, format=(None, "yaml"))

This also works with an array of format matching the number of cosmologies.

>>> cosmology_equal(mapping, yml, format=[True, "yaml"])