Sample CAMB Parameter file

Below is the sample parameter file supplied with CAMB. This sample file provides most of the configuration documentation supplied with the program. An excerpt from the readme file describing scaling and normalization is provided below the parameter file.

#Parameters for CAMB

#output_root is prefixed to output file names
output_root = test

#What to do
get_scalar_cls = T
get_vector_cls = F
get_tensor_cls = F
get_transfer   = F

#if do_lensing then scalar_output_file contains additional columns of l^4 C_l^{pp} and l^3 C_l^{pT}
#where p is the projected potential. Output lensed CMB Culs (without tensors) are in lensed_output_file below.
do_lensing     = T

# 0: linear, 1: non-linear matter power (HALOFIT), 2: non-linear CMB lensing (HALOFIT),
# 3: both non-linear matter power and CMB lensing (HALOFIT)
do_nonlinear = 0

#Maximum multipole and k*eta.
#  Note that C_ls near l_max are inaccurate (about 5%), go to 50 more than you need
#  Lensed power spectra are computed to l_max_scalar-100
#  To get accurate lensed BB need to have l_max_scalar>2000, k_eta_max_scalar > 10000
#  To get accurate lensing potential you also need k_eta_max_scalar > 10000
#  Otherwise k_eta_max_scalar=2*l_max_scalar usually suffices, or don't set to use default
l_max_scalar      = 2200
#k_eta_max_scalar  = 4000

#  Tensor settings should be less than or equal to the above
l_max_tensor      = 1500
k_eta_max_tensor  = 3000

#Main cosmological parameters, neutrino masses are assumed degenerate
# If use_phyical set physical densities in baryons, CDM and neutrinos + Omega_k
use_physical   = T
ombh2          = 0.0226
omch2          = 0.112
omnuh2         = 0.00064
omk            = 0
hubble         = 70

#effective equation of state parameter for dark energy
w              = -1
#constant comoving sound speed of the dark energy (1=quintessence)
cs2_lam        = 1

#varying w is not supported by default, compile with EQUATIONS=equations_ppf to use crossing PPF w-wa model:
#wa             = 0
##if use_tabulated_w read (a,w) from the following user-supplied file instead of above
#use_tabulated_w = F
#wafile = wa.dat

#if use_physical = F set parameters as here
#omega_baryon   = 0.0462
#omega_cdm      = 0.2538
#omega_lambda   = 0.7
#omega_neutrino = 0

temp_cmb           = 2.7255
helium_fraction    = 0.24

#for share_delta_neff = T, the fractional part of massless_neutrinos gives the change in the effective number
#(for QED + non-instantaneous decoupling)  i.e. the increase in neutrino temperature,
#so Neff = massless_neutrinos + sum(massive_neutrinos)
#For full neutrino parameter details see
massless_neutrinos = 2.046

#number of distinct mass eigenstates
nu_mass_eigenstates = 1
#array of the integer number of physical neutrinos per eigenstate, e.g. massive_neutrinos = 2 1
massive_neutrinos  = 1
#specify whether all neutrinos should have the same temperature, specified from fractional part of massless_neutrinos
share_delta_neff = T
#nu_mass_fractions specifies how Omeganu_h2 is shared between the eigenstates
#i.e. to indirectly specify the mass of each state; e.g. nu_mass_factions= 0.75 0.25
nu_mass_fractions = 1
#if share_delta_neff = F, specify explicitly the degeneracy for each state (e.g. for sterile with different temperature to active)
#(massless_neutrinos must be set to degeneracy for massless, i.e. massless_neutrinos does then not include Deleta_Neff from massive)
#if share_delta_neff=T then degeneracies is not given and set internally
#e.g. for massive_neutrinos = 2 1, this gives equal temperature to 4 neutrinos: nu_mass_degeneracies = 2.030 1.015, massless_neutrinos = 1.015
nu_mass_degeneracies =

#Initial power spectrum, amplitude, spectral index and running. Pivot k in Mpc^{-1}.
initial_power_num         = 1
pivot_scalar              = 0.05
pivot_tensor              = 0.05
scalar_amp(1)             = 2.1e-9
scalar_spectral_index(1)  = 0.96
scalar_nrun(1)            = 0
scalar_nrunrun(1)         = 0
tensor_spectral_index(1)  = 0
tensor_nrun(1)            = 0
#Three parameterizations (1,2,3) for tensors, see
tensor_parameterization   = 1
#ratio is that of the initial tens/scal power spectrum amplitudes, depending on parameterization
#for tensor_parameterization == 1, P_T = initial_ratio*scalar_amp*(k/pivot_tensor)^tensor_spectral_index
#for tensor_parameterization == 2, P_T = initial_ratio*P_s(pivot_tensor)*(k/pivot_tensor)^tensor_spectral_index
#Note that for general pivot scales and indices, tensor_parameterization==2 as P_T depending on n_s
initial_ratio(1)          = 1
#tensor_amp is used instead if tensor_parameterization == 3, P_T = tensor_amp *(k/pivot_tensor)^tensor_spectral_index
#tensor_amp(1)            = 4e-10

#note vector modes use the scalar settings above

#Reionization, ignored unless reionization = T, re_redshift measures where x_e=0.5
reionization         = T

re_use_optical_depth = T
re_optical_depth     = 0.09
#If re_use_optical_depth = F then use following, otherwise ignored
re_redshift          = 11
#width of reionization transition. CMBFAST model was similar to re_delta_redshift~0.5.
re_delta_redshift    = 1.5
#re_ionization_frac=-1 sets to become fully ionized using YE to get helium contribution
#Otherwise x_e varies from 0 to re_ionization_frac
re_ionization_frac   = -1

#RECFAST 1.5.x recombination parameters;
RECFAST_fudge = 1.14
RECFAST_fudge_He = 0.86
RECFAST_Heswitch = 6
RECFAST_Hswitch  = T

# CosmoMC parameters - compile with RECOMBINATION=cosmorec and link to CosmoMC to use these
# cosmorec_runmode== 0: CosmoMC run with diffusion
#                    1: CosmoMC run without diffusion
#                    2: RECFAST++ run (equivalent of the original RECFAST version)
#                    3: RECFAST++ run with correction function of Calumba & Thomas, 2010
# For 'cosmorec_accuracy' and 'cosmorec_fdm' see CosmoMC for explanation
#cosmorec_runmode        = 0
#cosmorec_accuracy       = 0
#cosmorec_fdm            = 0

#Initial scalar perturbation mode (adiabatic=1, CDM iso=2, Baryon iso=3,
# neutrino density iso =4, neutrino velocity iso = 5)
initial_condition   = 1
#If above is zero, use modes in the following (totally correlated) proportions
#Note: we assume all modes have the same initial power spectrum
initial_vector = -1 0 0 0 0

#For vector modes: 0 for regular (neutrino vorticity mode), 1 for magnetic
vector_mode = 0

COBE_normalize = F
##CMB_outputscale scales the output Culs
#To get MuK^2 set realistic initial amplitude (e.g. scalar_amp(1) = 2.3e-9 above) and
#otherwise for dimensionless transfer functions set scalar_amp(1)=1 and use
#CMB_outputscale = 1
CMB_outputscale = 7.42835025e12

#Transfer function settings, transfer_kmax=0.5 is enough for sigma_8
#transfer_k_per_logint=0 sets sensible non-even sampling;
#transfer_k_per_logint=5 samples fixed spacing in log-k
#transfer_interp_matterpower =T produces matter power in regular interpolated grid in log k;
# use transfer_interp_matterpower =F to output calculated values (e.g. for later interpolation)
transfer_high_precision = F
transfer_kmax           = 2
transfer_k_per_logint   = 0
transfer_num_redshifts  = 1
transfer_interp_matterpower = T
transfer_redshift(1)    = 0
transfer_filename(1)    = transfer_out.dat
#Matter power spectrum output against k/h in units of h^{-3} Mpc^3
transfer_matterpower(1) = matterpower.dat

#Output files not produced if blank. make camb_fits to use the FITS setting.
scalar_output_file = scalCls.dat
vector_output_file = vecCls.dat
tensor_output_file = tensCls.dat
total_output_file  = totCls.dat
lensed_output_file = lensedCls.dat
lensed_total_output_file  =lensedtotCls.dat
lens_potential_output_file = lenspotentialCls.dat
FITS_filename      = scalCls.fits

#Bispectrum parameters if required; primordial is currently only local model (fnl=1)
#lensing is fairly quick, primordial takes several minutes on quad core
do_lensing_bispectrum = F
do_primordial_bispectrum = F

#1 for just temperature, 2 with E
bispectrum_nfields = 1
#set slice non-zero to output slice b_{bispectrum_slice_base_L L L+delta}
bispectrum_slice_base_L = 0
#bispectrum_do_fisher estimates errors and correlations between bispectra
#note you need to compile with LAPACK and FISHER defined to use get the Fisher info
bispectrum_do_fisher= F
#Noise is in muK^2, e.g. 2e-4 roughly for Planck temperature
#Filename if you want to write full reduced bispectrum (at sampled values of l_1)
#Export alpha_l(r), beta_l(r) for local non-Gaussianity

##Optional parameters to control the computation speed,accuracy and feedback

#If feedback_level > 0 print out useful information computed about the model
feedback_level = 1

#write out various derived parameters
derived_parameters = T

# 1: curved correlation function, 2: flat correlation function, 3: inaccurate harmonic method
lensing_method = 1
accurate_BB = F

#massive_nu_approx: 0 - integrate distribution function
#                   1 - switch to series in velocity weight once non-relativistic
massive_nu_approx = 1

#Whether you are bothered about polarization.
accurate_polarization   = T

#Whether you are bothered about percent accuracy on EE from reionization
accurate_reionization   = T

#whether or not to include neutrinos in the tensor evolution equations
do_tensor_neutrinos     = T

#Whether to turn off small-scale late time radiation hierarchies (save time,v. accurate)
do_late_rad_truncation   = T

#Computation parameters
#if number_of_threads=0 assigned automatically
number_of_threads       = 0

#Default scalar accuracy is about 0.3% (except lensed BB) if high_accuracy_default=F
#If high_accuracy_default=T the default target accuracy is 0.1% at L>600 (with boost parameter=1 below)
#Try accuracy_boost=2, l_accuracy_boost=2 if you want to check stability/even higher accuracy
#Note increasing accuracy_boost parameters is very inefficient if you want higher accuracy,
#but high_accuracy_default is efficient


#Increase accuracy_boost to decrease time steps, use more k values,  etc.
#Decrease to speed up at cost of worse accuracy. Suggest 0.8 to 3.
accuracy_boost          = 1

#Larger to keep more terms in the hierarchy evolution.
l_accuracy_boost        = 1

#Increase to use more C_l values for interpolation.
#Increasing a bit will improve the polarization accuracy at l up to 200 -
#interpolation errors may be up to 3%
#Decrease to speed up non-flat models a bit
l_sample_boost          = 1

From the README file

As of November 2004 the supplied sample params.ini file produces results in μK2 from the given primordial curvature perturbation power (scalar_amp) on 0.05 MPc-1 scales. To get unnormalized dimensionless results set scalar_amp(1)=1 and CMB_outputscale=1 (as in previous CAMB versions). To compute lensed Cls you must set the normalization to some realistic value (the calculation is non-linear, so normalization matters).

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