Basic functions

Python CAMB interface (


Calculate results for specified parameters and return CAMBdata instance for getting results.

Parameters:paramsmodel.CAMBparams instance
Returns:CAMBdata instance
camb.get_background(params, no_thermo=False)[source]

Calculate background cosmology for specified parameters and return CAMBdata, ready to get derived parameters and use background functions like angular_diameter_distance().

  • paramsmodel.CAMBparams instance
  • no_thermo – set True if thermal and ionization history not required.

CAMBdata instance

camb.get_transfer_functions(params, only_time_sources=False)[source]

Calculate transfer functions for specified parameters and return CAMBdata instance for getting results and subsequently calculating power spectra.

  • paramsmodel.CAMBparams instance
  • only_time_sources – does not calculate the CMB l,k transfer functions and does not apply any non-linear correction scaling. Results with only_time_sources=True can therefore be used with different initial power spectra to get consistent non-linear lensed spectra.

CAMBdata instance

camb.set_params(cp=None, verbose=False, **params)[source]

Set all CAMB parameters at once, including parameters which are part of the CAMBparams structure, as well as global parameters.


cp = camb.set_params(ns=1, H0=67, ombh2=0.022, omch2=0.1, w=-0.95, Alens=1.2, lmax=2000,
                     WantTransfer=True, dark_energy_model='DarkEnergyPPF')

This is equivalent to:

cp = model.CAMBparams()
cp.DarkEnergy = DarkEnergyPPF()
cp.set_cosmology(H0=67, omch2=0.1, ombh2=0.022, Alens=1.2)
cp.WantTransfer = True

The wrapped functions are (in this order):

  • params – the values of the parameters
  • cp – use this CAMBparams instead of creating a new one
  • verbose – print out the equivalent set of commands

model.CAMBparams instance

camb.set_params_cosmomc(p, num_massive_neutrinos=1, neutrino_hierarchy='degenerate', halofit_version='mead', dark_energy_model='ppf', lmax=2500, lens_potential_accuracy=1, inpars=None)[source]

get CAMBParams for dictionary of cosmomc-named parameters assuming Planck 2018 defaults

  • p – dictionary of cosmomc parameters (e.g. from getdist.types.BestFit’s getParamDict() function)
  • num_massive_neutrinos – usually 1 if fixed mnu=0.06 eV, three if mnu varying
  • neutrino_hierarchy – hierarchy
  • halofit_version – name of the soecific Halofit model to use for non-linear modelling
  • dark_energy_model – ppf or fluid dark energy model
  • lmax – lmax for accuracy settings
  • lens_potential_accuracy – lensing accuracy parameter
  • inpars – optional input CAMBParams to set

camb.read_ini(ini_filename, no_validate=False)[source]

Get a model.CAMBparams instance using parameter specified in a .ini parameter file.

  • ini_filename – path of the .ini file to read
  • no_validate – do not pre-validate the ini file (faster, but may crash kernel if error)

model.CAMBparams instance

camb.get_matter_power_interpolator(params, zmin=0, zmax=10, nz_step=100, zs=None, kmax=10, nonlinear=True, var1=None, var2=None, hubble_units=True, k_hunit=True, return_z_k=False, k_per_logint=None, log_interp=True, extrap_kmax=None)[source]

Return a 2D spline interpolation object to evaluate matter power spectrum as function of z and k/h, e.g.

from camb import get_matter_power_interpolator
PK = get_matter_power_interpolator(params);
print('Power spectrum at z=0.5, k/h=0.1/Mpc is %s (Mpc/h)^3 '%(PK.P(0.5, 0.1)))

For a description of outputs for different var1, var2 see Matter power spectrum and matter transfer function variables. If you already have a CAMBdata result object, you can instead use get_matter_power_interpolator().

  • paramsmodel.CAMBparams instance
  • zmin – minimum z (use 0 or smaller than you want for good interpolation)
  • zmax – maximum z (use larger than you want for good interpolation)
  • nz_step – number of steps to sample in z (default max allowed is 100)
  • zs – instead of zmin,zmax, nz_step, can specific explicit array of z values to spline from
  • kmax – maximum k
  • nonlinear – include non-linear correction from halo model
  • var1 – variable i (index, or name of variable; default delta_tot)
  • var2 – variable j (index, or name of variable; default delta_tot)
  • hubble_units – if true, output power spectrum in \(({\rm Mpc}/h)^{3}\) units, otherwise \({\rm Mpc}^{3}\)
  • k_hunit – if true, matter power is a function of k/h, if false, just k (both \({\rm Mpc}^{-1}\) units)
  • return_z_k – if true, return interpolator, z, k where z, k are the grid used
  • k_per_logint – specific uniform sampling over log k (if not set, uses optimized irregular sampling)
  • log_interp – if true, interpolate log of power spectrum (unless any values are negative in which case ignored)
  • extrap_kmax – if set, use power law extrapolation beyond kmax to extrap_kmax (useful for tails of integrals)

An object PK based on RectBivariateSpline, that can be called with PK.P(z,kh) or PK(z,log(kh)) to get log matter power values. If return_z_k=True, instead return interpolator, z, k where z, k are the grid used.


Get age of universe for given set of parameters

Parameters:paramsmodel.CAMBparams instance
Returns:age of universe in gigayears
camb.get_zre_from_tau(params, tau)[source]

Get reionization redshift given optical depth tau


reionization redshift (or negative number if error)


Set the feedback level for internal CAMB calls

Parameters:level – zero for nothing, >1 for more
camb.run_ini(ini_filename, no_validate=False)[source]

Run the command line camb from a .ini file (producing text files as with the command line program). This does the same as the command line program, except global config parameters are not read and set (which does not change results in almost all cases).

  • ini_filename – .ini file to use
  • no_validate – do not pre-validate the ini file (faster, but may crash kernel if error)
camb.get_valid_numerical_params(transfer_only=False, **class_names)[source]

Get numerical parameter names that are valid input to set_params()

  • transfer_only – if True, exclude parameters that affect only initial power spectrum or non-linear model
  • class_names – class name parameters that will be used by model.CAMBparams.set_classes()

set of valid input parameter names for set_params()