Boltzmann codes: CAMB, CLASS compute twopoint angular correlation function
Boltzmann codes: CAMB, CLASS compute twopoint angular corre
I am struggling to use CAMB or CLASS to directly compute and plot the twopoint temperature correlation function C(theta). (See for example firstyear WMAP release, astroph/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 firstyear data product. I would like to plot the theoretical prediction C(theta) versus theta.
Naturally, I can manipulate the CAMB or CLASSgenerated 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?
Naturally, I can manipulate the CAMB or CLASSgenerated 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?

 Posts: 1379
 Joined: September 23 2004
 Affiliation: University of Sussex
 Contact:
Re: Boltzmann codes: CAMB, CLASS compute twopoint angular c
Not using CAMB (or CLASS AFAIK)  as you say, just calculate the CL and transform.
Boltzmann codes: CAMB, CLASS compute twopoint angular corre
@Antony Lewis
Thanks for the help!
Thanks for the help!
Boltzmann codes: CAMB, CLASS compute twopoint 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.
Thanks a lot. Good Luck.

 Posts: 1379
 Joined: September 23 2004
 Affiliation: University of Sussex
 Contact:
Re: Boltzmann codes: CAMB, CLASS compute twopoint 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:
http://camb.readthedocs.io/en/latest/correlations.html
BTW, CAMB now can calculate correlation functions for you, via the Python wrapper:
http://camb.readthedocs.io/en/latest/correlations.html