## pycamb BB power spectrum

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
yajing huang
Posts: 9
Joined: January 21 2015
Affiliation: Johns Hopkins University

### pycamb BB power spectrum

Hi,

I was using pycamb to calculate BB power spectrum up to l~200. I set:

params.WantTensor = True
params.NonLinear =2
params.AccurateBB=1

However, I found that the shape of the power spectrum (even at low l) depends greatly on lmax. To get accurate BB, I needed to set lmax to as great as ~3000. I was wondering if there is some other setting I can use to achieve accuracy without spending too much computing power.

Thanks,

Yajing

Antony Lewis
Posts: 1543
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: pycamb BB power spectrum

Yes, if you want the lensed BB accurate, which come from lensing of high-l EE and \phi\phi, you need to calculate the unlensed spectra to quite high lmax. (the non-linear corrections are also dependent on quite small scales)