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Commit bd951ba5 authored by Leo Pound Singer's avatar Leo Pound Singer

Add cosmological prior docstrings

parent 14b291a7
Pipeline #49553 failed with stages
in 9 minutes and 30 seconds
Cosmology (`ligo.skymap.postprocess.cosmology`)
.. automodule:: ligo.skymap.postprocess.cosmology
......@@ -7,6 +7,7 @@ Sky Map Postprocessing (`ligo.skymap.postprocess`)
:maxdepth: 1
......@@ -16,6 +16,11 @@
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
Cosmology-related utilities.
All functions in this module use the WMAP9 cosmological parameters.
import numpy as np
import astropy.cosmology
......@@ -26,8 +31,23 @@ cosmo = astropy.cosmology.default_cosmology.get_cosmology_from_string(
def dVC_dVL_for_z(z):
"""Ratio between the comoving volume element dVC and a
DL**2 prior at redshift z."""
r'''Ratio, :math:`\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,
:math:`\mathrm{d}V_C / \mathrm{d}z`, and the derivative of luminosity
distance in terms of redshift, :math:`\mathrm{d}D_L / \mathrm{d}z`, this is
expressed as:
.. math::
\frac{\mathrm{d}V_C}{\mathrm{d}V_L} =
{D_L}^2 \frac{\mathrm{d}D_L}{\mathrm{d}z}
Ok0 = cosmo.Ok0
DH = cosmo.hubble_distance
DM_by_DH = (cosmo.comoving_transverse_distance(z) / DH).value
......@@ -47,9 +67,12 @@ def dVC_dVL_for_z(z):
def z_for_DL(DL):
"""Redshift as a function of luminosity distance in Mpc."""
return astropy.cosmology.z_at_value(
cosmo.luminosity_distance, DL * u.Mpc)
def dVC_dVL_for_DL(DL):
"""Same as :meth:`dVC_dVL_for_z`, but as a function of luminosity
return dVC_dVL_for_z(z_for_DL(DL))
......@@ -16,7 +16,26 @@
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
Generate Chebyshev coefficients for BAYESTAR uniform-in-comoving-volume prior.
This is a lookup table for the BAYESTAR uniform-in-comoving-volume prior. The
BAYESTAR posterior distribution has a builtin prior that is uniform in naively
Euclidean luminosity distance space (proportional to DL^2). When we want to
switch to a prior that is uniform in comoving volume, we have to multiply by
the factor dVC/dVL, the differential comoving volume per unit Euclidean
luminosity volume.
The lookup table is in terms of the *natural logarithm* of the luminosity
distance and provides the *natural logarithm* of dVC/dVL. It consists of the
following constants:
dVC_dVL_tmin, dVC_dVL_tmax, dVC_dVL_dt
Minimum, maximum, and step size for a uniform grid in t = log(DL),
such that t[i] = dVC_dVL_tmin + i * dVC_dVL_dt.
Tabulated values of y = f(t) = log(dVC/dVL), such that y[i] = f(t[i]).
dVC_dVL_high_z_slope, dVC_dVL_high_z_intercept
Linear fit for extrapolating f(t) for t>dVC_dVL_tmax.
import argparse
import os
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