nbodykit.cosmology.cosmology module¶

class nbodykit.cosmology.cosmology.Cosmology(h=0.67556, T_cmb=2.7255, Omega_b=0.0482754208891869, Omega_cdm=0.26377065934278865, N_ur=None, m_ncdm=[0.06], P_k_max=10.0, P_z_max=100.0, gauge='synchronous', n_s=0.9667, nonlinear=False, verbose=False, **kwargs)[source]¶

Bases: object

A cosmology calculator based on the CLASS binding in classylss.

It is a collection of all method provided by the CLASS interfaces.

The individual interfaces can be accessed too, such that c.Spectra.get_transfer and c.get_transfer are identical.

Important

A default set of units is assumed. Those units are:

temperature: \(\mathrm{K}\)
distance: \(h^{-1} \mathrm{Mpc}\)
wavenumber: \(h \mathrm{Mpc}^{-1}\)
power: \(h^{-3} \mathrm{Mpc}^3\)
density: \(10^{10} (M_\odot/h) (Mpc/h)^{-3}\)
neutrino mass: \(\mathrm{eV}\)
time: \(\mathrm{Gyr}\)
H0: \((h^{-1} \mathrm{Mpc}) / (\mathrm{km/s})\)

Notes

The default configuration assumes a flat cosmology, \(\Omega_{0,k}=0\). Pass Omega_k in the extra keyword dictionary to change this value.
By default, a cosmological constant is assumed, with its density value inferred by the curvature condition.
Non-cosmological constant dark energy can be used by specifying the w0_fld, wa_fld, and/or Omega_fld values.
The sigma8 attribute can be set to the desired value, and the internal value of A_s will be automatically adjusted.

Parameters:

Parameters:	h (float) – the dimensionaless Hubble parameter T_cmb (float) – the temperature of the CMB in Kelvins Omega_b (float) – the current baryon density parameter, \(\Omega_{b,0}\) Omega_cdm (float) – the current cold dark matter density parameter, \(\Omega_{cdm,0}\) N_ur (float) – the number of ultra-relativistic (massless neutrino) species; the default number is inferred based on the number of massive neutrinos via the following logic: if you have respectively 1,2,3 massive neutrinos and use the default `T_ncdm` value (0.71611 K), designed to give m/omega of 93.14 eV, and you wish to have `N_eff=3.046` in the early universe, then `N_ur` is set to 2.0328, 1.0196, 0.00641, respectively. m_ncdm (list, None) – the masses (in eV) for all massive neutrino species; an empty list should be passed for no massive neutrinso. The default is a single massive neutrino with mass of 0.06 eV P_k_max (float) – the maximum `k` value to compute power spectrum results to, in units of \(h/Mpc\) P_z_max (float) – the maximum redshift to compute power spectrum results to gauge (str,) – either synchronous or newtonian n_s (float) – the tilt of the primordial power spectrum nonlinear (bool) – whether to compute nonlinear power spectrum results via HaloFit verbose (bool) – whether to turn on the default CLASS logging for all submodules **kwargs – extra keyword parameters to pass to CLASS; users should be wary of configuration options that may conflict with the base set of parameters

h (float) – the dimensionaless Hubble parameter
T_cmb (float) – the temperature of the CMB in Kelvins
Omega_b (float) – the current baryon density parameter, \(\Omega_{b,0}\)
Omega_cdm (float) – the current cold dark matter density parameter, \(\Omega_{cdm,0}\)
N_ur (float) – the number of ultra-relativistic (massless neutrino) species; the default number is inferred based on the number of massive neutrinos via the following logic: if you have respectively 1,2,3 massive neutrinos and use the default T_ncdm value (0.71611 K), designed to give m/omega of 93.14 eV, and you wish to have N_eff=3.046 in the early universe, then N_ur is set to 2.0328, 1.0196, 0.00641, respectively.
m_ncdm (list, None) – the masses (in eV) for all massive neutrino species; an empty list should be passed for no massive neutrinso. The default is a single massive neutrino with mass of 0.06 eV
P_k_max (float) – the maximum k value to compute power spectrum results to, in units of \(h/Mpc\)
P_z_max (float) – the maximum redshift to compute power spectrum results to
gauge (str,) – either synchronous or newtonian
n_s (float) – the tilt of the primordial power spectrum
nonlinear (bool) – whether to compute nonlinear power spectrum results via HaloFit
verbose (bool) – whether to turn on the default CLASS logging for all submodules
**kwargs – extra keyword parameters to pass to CLASS; users should be wary of configuration options that may conflict with the base set of parameters

Attributes

sigma8 The amplitude of matter fluctuations at \(z=0\) in a sphere of radius \(r = 8 \ h^{-1}\mathrm{Mpc}\).

Methods

`clone`(**kwargs)	Create a new cosmology based on modification of self, with the input keyword parameters changed.
`from_astropy`(cosmo, **kwargs)	Initialize and return a `Cosmology` object from a subclass of `astropy.cosmology.FLRW`.
`from_file`(filename, **kwargs)	Initialize a `Cosmology` object from the CLASS parameter file
`to_astropy`()	Initialize and return a subclass of `astropy.cosmology.FLRW` from the `Cosmology` class.

__dir__()[source]¶: a list of all members from all delegate classes

__getattr__(name)[source]¶: Find the proper delegate, initialize it, and run the method

__iter__()[source]¶: Allows dict() to be used on class.

clone(**kwargs)[source]¶

Create a new cosmology based on modification of self, with the input keyword parameters changed.

Parameters:	**kwargs – keyword parameters to adjust
Returns:	a copy of self, with the input `kwargs` adjusted
Return type:	`Cosmology`

dro = [<class 'classylss.astropy_compat.AstropyCompat'>, <class 'classylss.binding.Thermo'>, <class 'classylss.binding.Spectra'>, <class 'classylss.binding.Perturbs'>, <class 'classylss.binding.Primordial'>, <class 'classylss.binding.Background'>, <class 'classylss.binding.ClassEngine'>]¶

dro_dict = {'Primordial': <class 'classylss.binding.Primordial'>, 'Background': <class 'classylss.binding.Background'>, 'Perturbs': <class 'classylss.binding.Perturbs'>, 'Spectra': <class 'classylss.binding.Spectra'>, 'ClassEngine': <class 'classylss.binding.ClassEngine'>, 'Thermo': <class 'classylss.binding.Thermo'>, 'AstropyCompat': <class 'classylss.astropy_compat.AstropyCompat'>}¶

classmethod from_astropy(cosmo, **kwargs)[source]¶

Initialize and return a Cosmology object from a subclass of astropy.cosmology.FLRW.

Parameters:	cosmo (subclass of `astropy.cosmology.FLRW`.) – the astropy cosmology instance **kwargs – extra keyword parameters to pass when initializing
Returns:	the initialized cosmology object
Return type:	`Cosmology`

classmethod from_file(filename, **kwargs)[source]¶

Initialize a Cosmology object from the CLASS parameter file

Parameters:	filename (str) – the name of the parameter file to read

sigma8¶

The amplitude of matter fluctuations at \(z=0\) in a sphere of radius \(r = 8 \ h^{-1}\mathrm{Mpc}\).

This is not an input CLASS parameter, but users can set this parameter and the scalar amplitude A_s will be internally adjusted to achieve the desired sigma8.

to_astropy()[source]¶

Initialize and return a subclass of astropy.cosmology.FLRW from the Cosmology class.

Returns:	the astropy class holding the cosmology values
Return type:	subclass of `astropy.cosmology.FLRW`

nbodykit.cosmology.cosmology.astropy_to_dict(cosmo)[source]¶: Convert an astropy cosmology object to a dictionary of parameters suitable for initializing a Cosmology object.

nbodykit.cosmology.cosmology.sanitize_class_params(cosmo, pars)[source]¶

Given a dictionary of CLASS parameters, construct the args dict and kwargs dict that can used to initialize a Cosmology class, accounting for any possible conflicts.

The args dict holds the main (named) __init__ keywords, and the kwargs holds all of the extra keywords.

nbodykit.cosmology.cosmology.set_sigma8(cosmo, sigma8, inplace=False)[source]¶

Return a clone of the input Cosmology object, with the sigma8 value set to the specified value.

Parameters:	cosmo (Cosmology) – the input cosmology object sigma8 (float) – the desired sigma8 value inplace (bool, optional) – if `True`, update sigma8 of the input `cosmo` object, else return a new Cosmology object

nbodykit.cosmology.cosmology.verify_parameters(args, extra)[source]¶: Verify the input parameters to a Cosmology object and set various default values.