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

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Evan B
Posts: 13
Joined: February 27 2015
Affiliation: student

### Boltzmann codes: CAMB, CLASS compute two-point angular corre

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 C_l 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?

Antony Lewis
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Joined: September 23 2004
Affiliation: University of Sussex
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### Re: Boltzmann codes: CAMB, CLASS compute two-point angular c

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

Evan B
Posts: 13
Joined: February 27 2015
Affiliation: student

### Boltzmann codes: CAMB, CLASS compute two-point angular corre

@Antony Lewis

Thanks for the help!

Bob Zou
Posts: 5
Joined: July 21 2016
Affiliation: Beijing Institute of Technology

### Boltzmann codes: CAMB, CLASS compute two-point angular corre

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.

Antony Lewis
Posts: 1472
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: Boltzmann codes: CAMB, CLASS compute two-point angular c

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: