### CAMB: Can't recover sigma-8 from published table

Posted:

**July 05 2020**Hi all,

I am trying to get a matter power-spectrum prediction out of CAMB to test some simulation results. Before that I wanted to verify that I can run CAMB and get an output that matches the published Planck-13 values.

I am especially interested in the last column of table 5 of https://arxiv.org/abs/1303.5076.

I use as CAMB input:
(All the rest is pretty standard but happy to provide more... can't attach my full file to the post)

but when asking CAMB what sigma_8 at z=0
should be I get: 0.84117.

This differs from the reported value in the table (0.8288).

I am surely doing something silly here in the way I ran CAMB. I have tried changing some of the accuracy parameters or range parameters but could not see any difference in the outcome.

Any help figuring out what I am doing wrong here would be greatly appreciated.

Thanks!

Matthieu

I am trying to get a matter power-spectrum prediction out of CAMB to test some simulation results. Before that I wanted to verify that I can run CAMB and get an output that matches the published Planck-13 values.

I am especially interested in the last column of table 5 of https://arxiv.org/abs/1303.5076.

I use as CAMB input:

Code: Select all

```
ombh2 = 0.022161
omch2 = 0.11889
omnuh2 = 0
omk = 0
hubble = 67.77
initial_power_num = 1
pivot_scalar = 0.05
pivot_tensor = 0.05
scalar_amp = 2.21381e-9 # ln(10^10 A_s) = 3.0973
scalar_spectral_index = 0.9611
reionization = T
re_use_optical_depth = T
re_optical_depth = 0.0952
massless_neutrinos = 3.046
massive_neutrinos = 0
share_delta_neff = T
```

but when asking CAMB what sigma_8 at z=0

Code: Select all

```
pars = camb.read_ini('EAGLE_2013.ini')
pars.set_matter_power(redshifts=[0.], kmax=30.0)
pars.NonLinear = model.NonLinear_both
results = camb.get_results(pars)
results.calc_power_spectra(pars)
sigma_8_z0_1 = results.get_sigma8_0()
```

This differs from the reported value in the table (0.8288).

I am surely doing something silly here in the way I ran CAMB. I have tried changing some of the accuracy parameters or range parameters but could not see any difference in the outcome.

Any help figuring out what I am doing wrong here would be greatly appreciated.

Thanks!

Matthieu