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Meaning of different chi-squares in COSMOMC
 
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Brajesh Gupt



Joined: 04 Jan 2015
Posts: 6
Affiliation: Pennsylvania State University

PostPosted: September 02 2016  Reply with quote

Hi,

After running getdist, one usually gets the several different types of chi-square values. What do they mean? For example, I get (I show only the best fit values) following 5 types:
Code:

     0.2579038E+02     \chi^2_{\rm lensing}
     0.7639290E+03     \chi^2_{\rm plik}
     0.1049659E+05     \chi^2_{\rm lowTEB}
     0.2068837E+01     \chi^2_{\rm prior}
     0.1128631E+05    \chi^2_{\rm CMB}


While comparing two models which one should I use?

Any insight will be very helpful.

Thanks,
Brajesh
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Stéphane Ilic



Joined: 11 Feb 2014
Posts: 15
Affiliation: IRAP Toulouse

PostPosted: September 30 2016  Reply with quote

Hello Brajesh,

Those are the different contributions to the total likelihood/chi2.

From what you copy-pasted, I guess that you ran a MCMC chain with the Planck low-ell ("lowTEB"), high-ell ("plik"), and lensing ("lensing"). The "prior" chi2 is, you guessed it, the contribution coming from the priors you have chosen. The "CMB" chi2 is just the sum of all CMB-related chi2, i.e. "lowTEB+plik+lensing".

You should most likely use the total chi2/likelihood when comparing models...

Cheers,
Stephane
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