Different chi2 evaluate sampler cobaya CAMB vs CLASS

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Helena Garcia
Posts: 25
Joined: October 05 2021
Affiliation: UCI

Different chi2 evaluate sampler cobaya CAMB vs CLASS

Post by Helena Garcia » January 19 2024

I am running the evaluate sampler in cobaya fixing all the LCDM and nuisance parameters of the likelihoods to the same values for both CLASS and CAMB (all of these parameters are set to the same values in both codes: logA,ns,ombh2,omch2,tau,A_planck,calib_100T,calib_217T,A_cib_217,xi_sz_cib,A_sz,ksz_norm, gal545_A_100,gal545_A_143 , gal545_A_143_217, gal545_A_217, ps_A_100_100, ps_A_143_143,ps_A_143_217, ps_A_217_217, galf_TE_A_100, galf_TE_A_100_143, galf_TE_A_100_217, galf_TE_A_143 , galf_TE_A_143_217, galf_TE_A_217, As,omegam,omegamh2,omega_de,Yhe).
I am also setting in CAMB nnu to 3.044 and mnu to and equivalently in CLASS N_ur to 3.044 and N_ncdm to 0
Adding Planck and BAODR16 likelihoods I am getting a difference in the chi2 of 3.36880000000019. The derived parameters zre, sigma 8, age, and rdrag are also different. I wanted to check that I obtained the same chi2 when running both codes with the same likelihoods but I didn't. Where can be the problem?
Thanks in advance!

Antony Lewis
Posts: 1930
Joined: September 23 2004
Affiliation: University of Sussex
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Re: Different chi2 evaluate sampler cobaya CAMB vs CLASS

Post by Antony Lewis » January 19 2024

Different thetastar/approx thetastar?

Helena Garcia
Posts: 25
Joined: October 05 2021
Affiliation: UCI

Re: Different chi2 evaluate sampler cobaya CAMB vs CLASS

Post by Helena Garcia » January 19 2024

I am fixing H0 instead of theta, since the definition of theta for CLASS/CAMB is different.
The output .txt file doesn't provide theta_star, can I add something to the input .yaml file so I get the value od theta_star in the output and compare their value?

Antony Lewis
Posts: 1930
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: Different chi2 evaluate sampler cobaya CAMB vs CLASS

Post by Antony Lewis » January 19 2024

H0 should be fine, but it's not in your list of parameters.

Helena Garcia
Posts: 25
Joined: October 05 2021
Affiliation: UCI

Re: Different chi2 evaluate sampler cobaya CAMB vs CLASS

Post by Helena Garcia » January 21 2024

Sorry, I missed to include it. H0 is also fixed to the same value in both .yaml input files for CLASS and CAMB. Any idea where is the difference in the chi2 coming from? Thanks!

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