# Global settings and defaults¶

The global settings used in Colossus are split into two modules. The settings module contains user-defined settings that control how Colossus runs and interacts with the system. In contrast, the defaults module contains default values for physical parameters that influence the output of numerous Colossus routines, as well as standard models used for physical quantities (such as the default concentration module). For physical constants, please see the constants module.

## Settings¶

Global settings used across Colossus.

settings.BASE_DIR = None

The directory in which Colossus stores files, e.g. cache files (without a backslash at the end). If None, the home directory is used. If a home directory cannot be identified (an extremely rare case), the code directory is used.

settings.PERSISTENCE = 'rw'

This parameter determines whether Colossus stores persistent files such as the cosmology cache. The parameter can take on any combination of read ('r') and write ('w'), such as 'rw' (read and write, the default), 'r' (read only), 'w' (write only), or '' (no persistence). Note that this parameter is used as a default, but can still be changed for individual Colossus modules or objects, such as cosmology objects.

settings.PERSISTENCE_OLDEST_VERSION = '1.2.10'

If the colossus version that wrote a persistent quantitity was older than this version, the quantity is re-computed and the old file is removed. The version is increased whenever a numerical change affects persistent quantities to ensure that no outdated data is kept.

## Defaults¶

Global defaults used across Colossus.

defaults.COSMOLOGY_TCMB0 = 2.7255

The default CMB temperature in Kelvin.

defaults.COSMOLOGY_NEFF = 3.046

The default number of effective neutrino species.

defaults.POWER_SPECTRUM_MODEL = 'eisenstein98'

The default power spectrum model.

defaults.HALO_BIAS_MODEL = 'tinker10'

The default halo bias model.

defaults.HALO_MASS_FUNCTION_MODEL = 'watson13'

The default halo mass function model.

defaults.HALO_CONCENTRATION_MODEL = 'diemer19'

The default concentration model.

defaults.HALO_CONCENTRATION_STATISTIC = 'median'

The default statistic used (mean or median). This only applies to those models that distinguish between mean and median statistics.

defaults.HALO_MASS_CONVERSION_PROFILE = 'nfw'

The default profile used for mass conversions. Whenever spherical overdensity mass definitions are converted into one another, we have to assume a form of the density profile. The simplicity of the Navarro-Frenk-White profile makes this computation efficient.

defaults.HALO_SPLASHBACK_MODEL = 'diemer17'

The default model for the splashback radius.

defaults.HALO_SPLASHBACK_STATISTIC = 'median'

The default statistic used (mean or median). This only applies to splashback models that distinguish between mean and median statistics.

defaults.HALO_SPLASHBACK_RSPDEF = 'mean'

The default definition of Rsp used. This only applies to splashback models that distinguish between different definitions.

defaults.PS_ARGS = {'model': 'eisenstein98', 'path': None}

The default arguments to be passed to the power spectrum function. This argument list cannot be empty by default because some functions store data tables depending on the underlying power spectrum.

defaults.SIGMA_ARGS = {}

The default arguments to be passed to the variance function.

defaults.DELTAC_ARGS = {}

The default arguments to be passed to the collapse overdensity function.

defaults.HALO_PROFILE_ENCLOSED_MASS_ACCURACY = 1e-06

Integration accuracy for enclosed mass.

defaults.HALO_PROFILE_SURFACE_DENSITY_ACCURACY = 0.0001

Integration accuracy for surface density.

defaults.HALO_PROFILE_SURFACE_DENSITY_MAX_R_INTERPOLATE = 100000000.0

Radius to which the surface density is integrated when interpolating the density.

defaults.HALO_PROFILE_SURFACE_DENSITY_MAX_R_INTEGRATE = 1e+20

Radius to which the surface density is integrated when evaluating the density exactly.

defaults.HALO_PROFILE_DELTA_SIGMA_MIN_R_INTERPOLATE = 1e-06

Radius from which the surface density is averaged to compute DeltaSigma.

defaults.HALO_PRPFOLE_DK14_SELECTED_BY = 'M'

The constructor of the Diemer & Kravtsov 2014 profile sets the profile parameters to either predict the mean profile of halos selected by their mass (M) or mass accretion rate and mass (Gamma).

defaults.HALO_PROFILE_DK14_PL_NORM = 1.0

The default normalization of the power-law outer profile for the DK14 profile.

defaults.HALO_PROFILE_DK14_PL_SLOPE = 1.5

The default slope of the power-law outer profile for the DK14 profile.

defaults.HALO_PROFILE_DK14_ACC_WARN = 0.01

If the desired halo mass cannot be matched with a DK14 profile to better than this accuracy, a warning is displayed.

defaults.HALO_PROFILE_DK14_ACC_ERR = 0.05

If the desired halo mass cannot be matched with a DK14 profile to better than this accuracy, an exception is raised.

defaults.HALO_PROFILE_OUTER_PL_MAXRHO = 1000.0

The default maximum density the power-law outer profile term can contribute to the total density, in units of the mean matter density. If this number is set too high, the power-law profile can lead to a spurious density contribution at very small radii, if it is set too high the power-law term will not contribute at all.

defaults.MCMC_N_WALKERS = 100

The number of chains (called walkers) run in parallel.

defaults.MCMC_INITIAL_STEP = 0.1

A guess at the initial step taken by the walkers.

defaults.MCMC_CONVERGENCE_STEP = 100

Test the convergence of the MCMC chains every n steps.

defaults.MCMC_CONVERGED_GR = 0.01

Take the chains to have converged when the Gelman-Rubin statistic is smaller than this number in all parameters.

defaults.MCMC_OUTPUT_EVERY_N = 100

Output the current state of the chain every n steps.