# Cosmology (ligo.skymap.postprocess.cosmology)¶

Cosmology-related utilities.

All functions in this module use the Planck15 cosmological parameters.

ligo.skymap.postprocess.cosmology.dVC_dVL_for_DL(DL)[source] [edit on github]

Same as dVC_dVL_for_z(), but as a function of luminosity distance.

ligo.skymap.postprocess.cosmology.dVC_dVL_for_z(z)[source] [edit on github]

Ratio, $$\mathrm{d}V_C / \mathrm{d}V_L$$, between the comoving volume element and a naively Euclidean volume element in luminosity distance space; given as a function of redshift.

Given the differential comoving volume per unit redshift, $$\mathrm{d}V_C / \mathrm{d}z$$, and the derivative of luminosity distance in terms of redshift, $$\mathrm{d}D_L / \mathrm{d}z$$, this is expressed as:

$\frac{\mathrm{d}V_C}{\mathrm{d}V_L} = \frac{\mathrm{d}V_C}{\mathrm{d}z} \left( {D_L}^2 \frac{\mathrm{d}D_L}{\mathrm{d}z} \right)^{-1}.$