## clxg for lcdm

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Omar Ruiz Macias
Posts: 10
Joined: February 15 2014
Affiliation: Cinvestav

### clxg for lcdm

Hi everyone,

I have a question about clxg (photons) perturbations. I was comparing the CAMB outcome using w=-1 (labeled 'clxg_lcdm ') and w=-0.99999999999 (labeled 'clxg_lcdm_false'). Of course, I was expecting the spectra to be indistinguishable and they are. However, checking the clxg as function of the scale factor (a), I have found the difference shown in the figure.

clxg_a_lcdm.png

What may be the reason for this difference? And, Why it takes place at this particular value of a?

Antony Lewis
Posts: 1534
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: clxg for lcdm

Is this using equations.f90 or equations_ppf.f90?

Omar Ruiz Macias
Posts: 10
Joined: February 15 2014
Affiliation: Cinvestav

### clxg for lcdm

It's using 'equations.f90' and 'fixq = 1._dl'.

Antony Lewis
Posts: 1534
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: clxg for lcdm

I think you are probably plotting different things here. With do_late_rad_truncation = T, the photon perturbations are not calculated at late time, so the array element you are outputting will be something else (dark energy perturbation or something else, depending on whether w=-1 and hence whether there are any dark energy perturbations).

The best way to plot parameter evolution is to use the python wrapper

Code: Select all

from matplotlib import pyplot as plt
import camb
import numpy as np

pars = camb.set_params&#40;H0=67.5, ombh2=0.022, omch2=0.122, As=2e-9, ns=0.95&#41;
data= camb.get_background&#40;pars&#41;

a=10**&#40;np.linspace&#40;-8, 0, 500&#41;&#41;
z = 1/a -1
eta = data.conformal_time&#40;z&#41;
ev = data.get_time_evolution&#40;1., eta, &#91;'delta_photon'&#93;&#41;
plt.loglog&#40;a, np.abs&#40;ev&#41;&#41;

Omar Ruiz Macias
Posts: 10
Joined: February 15 2014
Affiliation: Cinvestav

### clxg for lcdm

thank you, Antony. Now it calculates the photon perturbations at late time.