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 Cls (without tensors) are in lensed_output_file below.
do_lensing     = F

# 0: linear, 1: non-linear matter power (HALOFIT), 2: non-linear 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-250 where accurate at %-level
#  For high accuracy lensed spectra set l_max_scalar = (l you need) + 500
#  To get accurate lensed BB need to have l_max_scalar>2000, k_eta_max_scalar > 10000
#  Otherwise k_eta_max_scalar=2*l_max_scalar usually suffices
l_max_scalar      = 2000
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 phyiscal densities in baryone, CDM and neutrinos + Omega_k
use_physical   = T
ombh2          = 0.0226
omch2          = 0.114
omnuh2         = 0
omk            = 0
hubble         = 70
#effective equation of state parameter for dark energy, assumed constant
w              = -1
#constant comoving sound speed of the dark energy (1=quintessence)
cs2_lam        = 1

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

#massless_neutrinos is the effective number (for QED + non-instantaneous decoupling)
temp_cmb           = 2.725
helium_fraction    = 0.24
massless_neutrinos = 3.04
massive_neutrinos  = 0

#Reionization (assumed sharp), ignored unless reionization = T
reionization         = T
re_use_optical_depth = F
re_optical_depth     = 0.09
#If re_use_optical_depth = F then use following, otherwise ignored
re_redshift          = 11
re_ionization_frac   = 1

#Initial power spectrum, amplitude, spectral index and running
initial_power_num         = 1
scalar_amp(1)             = 2.46e-9
scalar_spectral_index(1)  = 0.96
scalar_nrun(1)            = 0
tensor_spectral_index(1)  = 0
#ratio is that of the initial tens/scal power spectrum amplitudes
initial_ratio(1)          = 1
#note vector modes use the scalar settings above

#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

#Normalization
COBE_normalize = F
##CMB_outputscale scales the output Cls
#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 = 7.4311e12

#Transfer function settings, transfer_kmax=0.5 is enough for sigma_8
transfer_high_precision = F
transfer_kmax           = 2
transfer_k_per_logint   = 5
transfer_num_redshifts  = 1
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 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
FITS_filename      = scalCls.fits

##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

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

#Recombination calculation: 1: RECFAST, 2: RECFAST+astro-ph/0501672 corrections
recombination = 1

#massive_nu_approx: 0 - integrate distribution function
#                   1 - switch to series in velocity weight once non-relativistic
#                   2 - use fast approximate scheme (CMB only- accurate for light neutrinos)
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   = F

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

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

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

#Default scalar accuracy is about 0.3% (except lensed BB). 
#For 0.1%-level try accuracy_boost=2, l_accuracy_boost=2.

#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

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 C_ls you must set the normalization to some realistic value (the calculation is non-linear, so normalization matters).