# nbodykit.cosmology.cosmology¶

Functions

 astropy_to_dict(cosmo) Convert an astropy cosmology object to a dictionary of parameters suitable for initializing a Cosmology object. check_args(args) check_deprecated_init(args, kwargs) Check if kwargs uses the (now deprecated) signature of Cosmology prior to version 0.2.6. compile_args(args) Compile the input args of Cosmology object to the input parameters (pars) to a Cosmology object. find_eqcls(key) merge_args(args, moreargs) merge moreargs into args. Decorator that adds the _user_kwargs attribute to the class to track which arguments the user actually supplied.

Classes

 Cosmology([h, T0_cmb, Omega0_b, Omega0_cdm, …]) A cosmology calculator based on the CLASS binding in classylss.
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.check_deprecated_init(args, kwargs)[source]

Check if kwargs uses the (now deprecated) signature of Cosmology prior to version 0.2.6.

If using the deprecated syntax, this returns the necessary arguments for the new signature, and None otherwise.

nbodykit.cosmology.cosmology.compile_args(args)[source]

Compile the input args of Cosmology object to the input parameters (pars) to a Cosmology object.

A variety of defaults are set to tune CLASS for quantities used in large scale structures.

Difference between pars and args:
• anything that is valid pars is also valid args.

• after replacing our customizations in args, we get pars.

Note that CLASS will check for additional conflicts.

nbodykit.cosmology.cosmology.merge_args(args, moreargs)[source]

merge moreargs into args.

Those defined in moreargs takes priority than those defined in args.

nbodykit.cosmology.cosmology.store_user_kwargs()[source]

Decorator that adds the _user_kwargs attribute to the class to track which arguments the user actually supplied.

class nbodykit.cosmology.cosmology.Cosmology(h=0.67556, T0_cmb=2.7255, Omega0_b=0.0482754208891869, Omega0_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]

A cosmology calculator based on the CLASS binding in classylss.

It is a collection of all method provided by the CLASS interfaces. The object is immutable. To obtain an instance with a new set of parameters use clone() or match().

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: $$10^{10} (M_\odot/h) (\mathrm{Mpc}/h)^{-3}$$

• neutrino mass: $$\mathrm{eV}$$

• time: $$\mathrm{Gyr}$$

• $$H_0$$: $$(\mathrm{km} \ \mathrm{s^{-1}}) / (h^{-1} \ \mathrm{Mpc})$$

Notes

• The default configuration assumes a flat cosmology, $$\Omega_{0,k}=0$$. Pass Omega0_k as a keyword to specify the desired non-flat curvature.

• For consistency of variable names, the present day values can be passed with or without ‘0’ postfix, e.g., Omega0_cdm is translated to Omega_cdm as CLASS always uses the names without 0 as input parameters.

• By default, a cosmological constant (Omega0_lambda) 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.

• To pass in CLASS parameters that are not valid Python argument names, use the dictionary/keyword arguments trick, e.g. Cosmology(..., **{'temperature contributions': 'y'})

• Cosmology(**dict(c)) is not supposed to work; use Cosmology.from_dict(dict(c)).

Parameters
• h (float) – the dimensionless Hubble parameter

• T0_cmb (float) – the temperature of the CMB in Kelvins

• Omega0_b (float) – the current baryon density parameter, $$\Omega_{b,0}$$. Currently unrealistic cosmology where Omega_b == 0 is not supported.

• Omega0_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 neutrinos. 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. Mainly used to pass-in parameter names that are not valid Python function argument names, e.g. temperature contributions, or number count contributions. Users should be wary of configuration options that may conflict with the base set of parameters. To override parameters, chain the result with clone().

Attributes
Omega0_cb

The total density of CDM and Baryon.

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_dict(pars) Creates a Cosmology from a pars dictionary. from_file(filename, **kwargs) Initialize a Cosmology object from the CLASS parameter file match([sigma8, Omega0_cb, Omega0_m]) Creates a new cosmology that matches a derived parameter. Initialize and return a subclass of astropy.cosmology.FLRW from the Cosmology class.

Attributes

Methods

property Omega0_cb

The total density of CDM and Baryon.

This is not an input CLASS parameter. To scale Omega0_cb, use match().

__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. Use from_dict() to reconstruct an instance.

__str__()[source]

Return a dict string when printed

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

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; they shall not be in conflict with the parameters inferred from cosmo. To override parameters, chain the result with clone().

Returns

the initialized cosmology object

Return type

Cosmology

classmethod from_dict(pars)[source]

Creates a Cosmology from a pars dictionary.

This is a rather ‘raw’ API. The dictionary must be readable by ClassEngine. Unlike Cosmology(**args), pars must not contain any convenient names defined here.

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

• **kwargs – extra keyword parameters to pass when initializing; they shall not be in conflict with the parameters inferred from cosmo. To override parameters, chain the result with clone().

match(sigma8=None, Omega0_cb=None, Omega0_m=None)[source]

Creates a new cosmology that matches a derived parameter. This is different from clone, where CLASS parameters are used.

Note that we only supoort matching one derived parameter at a time, because the matching is in general non-commutable.

Parameters
• sigma8 (float or None) – We scale the scalar amplitude A_s to achieve the desired sigma8.

• Omega0_cb (float or None) – Desired total energy density of CDM and baryon.

• Omega0_m (float or None) – Desired total energy density of matter-like components (included ncdm)

Returns

Return type

A new cosmology parameter where the derived parameter matches the given constrain.

property 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. To scale sigma8, use match(), which adjusts scalar amplitude A_s 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