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Boltzmann codes: CAMB, CLASS compute two-point angular correlation function
 
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Evan B



Joined: 27 Feb 2015
Posts: 13
Affiliation: student

PostPosted: May 04 2015  Reply with quote

I am struggling to use CAMB or CLASS to directly compute and plot the two-point temperature correlation function C(theta). (See for example first-year WMAP release, astro-ph/0302207v3, equations (5) and (6) in Section 7. Full derivation found in Durrer 2008 textbook "The Cosmic Microwave Background", equation 2.240.) The measured quantity was released as a WMAP first-year data product. I would like to plot the theoretical prediction C(theta) versus theta.

Naturally, I can manipulate the CAMB- or CLASS-generated outputs Cl and ell in order to calculate this expression. I could then convert ell values into theta, and plot the results. However, I would ideally like to directly compute C(theta) using Boltzmann codes. Is there a method to do this?
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1291
Affiliation: University of Sussex

PostPosted: May 05 2015  Reply with quote

Not using CAMB (or CLASS AFAIK) - as you say, just calculate the CL and transform.
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Evan B



Joined: 27 Feb 2015
Posts: 13
Affiliation: student

PostPosted: May 07 2015  Reply with quote

@Antony Lewis

Thanks for the help!
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Bob Zou



Joined: 21 Jul 2016
Posts: 4
Affiliation: Beijing Institute of Technology

PostPosted: September 18 2017  Reply with quote

Hi, Here CLASS was mentioned. We know CAMB and CLASS are both Boltzmann solver, So can anyone help summarising what more physics that CLASS can bring us? I mean if they have completely same functions, why efforts were paied to accomplish one thing twice?
Thanks a lot. Good Luck.
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1291
Affiliation: University of Sussex

PostPosted: September 18 2017  Reply with quote

The two codes basically implement the same physics. But they support a slightly different range of extensions/things you can calculate (e.g. CLASS makes it easier to add additional species, CAMB supports HMCode and has more things related to bispectra and CMB lensing). CAMB devel branch is similar to CLASSgal, but I don't know how they compare in detail.

BTW, CAMB now can calculate correlation functions for you, via the Python wrapper:

http://camb.readthedocs.io/en/latest/correlations.html
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