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Difference between CAMB and WMAP3 (Pt. II)
 
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A Stewart



Joined: 27 Sep 2007
Posts: 5
Affiliation: McGill University

PostPosted: October 12 2007  Reply with quote

Hi all,

I am new to CAMB and as a test I am just trying to reproduce the WMAP3 results for lcdm+tens model using the parameters given here.

When I plot the totCls.dat file output by CAMB along with the one given on the LAMBDA website I see a large difference around l<100. Can anyone explain whether this is normal or suggest a fix?

I have changed both k_0_scalar and k_0_tensor to 0.002 in power_tilt.f90. I am taking nT = -r / 8.



Here is my params.ini file:

Code:

#Parameters for CAMB

#output_root is prefixed to output file names
output_root = test_lcdm_tens

#What to do
get_scalar_cls = T
get_vector_cls = F
get_tensor_cls = T
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          = 0.0233
omch2          = 0.0962
omnuh2         = 0
omk            = 0
hubble         = 78.7
#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   = 0.0376
#omega_cdm      = 0.1594
#omega_lambda   = 0.803
#omega_neutrino = 0

#massless_neutrinos is the effective number (for QED + non-instantaneous decoupling)
temp_cmb           = 2.726
helium_fraction    = 0.24
massless_neutrinos = 3.04
massive_neutrinos  = 0

#Neutrino mass splittings
nu_mass_eigenstates = 1
#nu_mass_degeneracies = 0 sets nu_mass_degeneracies = massive_neutrinos
#otherwise should be an array
#e.g. for 3 neutrinos with 2 non-degenerate eigenstates, nu_mass_degeneracies = 2 1
nu_mass_degeneracies = 0 
#Fraction of total omega_nu h^2 accounted for by each eigenstate, eg. 0.5 0.5
nu_mass_fractions = 1


#Reionization (assumed sharp), ignored unless reionization = T
reionization         = T
re_use_optical_depth = T
re_optical_depth     = 0.090
#If re_use_optical_depth = F then use following, otherwise ignored
re_redshift          = 10.5
re_ionization_frac   = 1

#Initial power spectrum, amplitude, spectral index and running
initial_power_num         = 1
scalar_amp(1)             = 21.0e-10
scalar_spectral_index(1)  = 0.984
scalar_nrun(1)            = 0
tensor_spectral_index(1)  = -0.081
#ratio is that of the initial tens/scal power spectrum amplitudes
initial_ratio(1)          = 0.65
#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_k_per_logint=0 sets sensible non-even sampling;
#transfer_k_per_logint=5 samples fixed spacing in log-k
transfer_high_precision = F
transfer_kmax           = 2
transfer_k_per_logint   = 0
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)
#                   3 - intelligently use the best accurate method
massive_nu_approx = 3

#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_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).
#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          = 2

#Larger to keep more terms in the hierarchy evolution.
l_accuracy_boost        = 2

#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
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Ben Gold



Joined: 25 Sep 2004
Posts: 97
Affiliation: University of Minnesota

PostPosted: October 14 2007  Reply with quote

The parameters given in the table aren't for the "best-fit" C_\ell, they're the means over the chain. For LCDM+tens the best-fit model has a slightly smaller ΩΛ, closer to 0.777 (not 0.803, which is the mean), which explains the difference at low \ell.

If you really want the "best-fit" parameters you'll need to download the chain files.
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A Stewart



Joined: 27 Sep 2007
Posts: 5
Affiliation: McGill University

PostPosted: October 15 2007  Reply with quote

So, I guess that will involve running getdist from the COSMOMC package on those chain files. Is there anywhere that the actual "best-fit" parameters used are summarzied without having to install COSMOMC?

Sorry I think I should have posted this in the software thread.
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Ben Gold



Joined: 25 Sep 2004
Posts: 97
Affiliation: University of Minnesota

PostPosted: October 23 2007  Reply with quote

The best-fit isn't hard to find from the chain files, just look for the line with the lowest -ln(L) and read off the parameters. From the command line you can do something like
Code:

sort -n -k 2 chainfile.txt | head -1


I'll make the suggestion that in the future the best-fit params be summarized somewhere more obvious.
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