## CAMB: computing logarithmic growth rate "f"

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Andreu Font-Ribera
Posts: 2
Joined: October 17 2016
Affiliation: UCL

### CAMB: computing logarithmic growth rate "f"

Hi - I was looking for a way to compute the logarithmic growth rate "f(z)" , and Pablo Lemos pointed me to the following function in CAMB.

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 sigma2_vdelta_8 – array of v-delta8 correlation, so sigma2_vdelta_8/sigma_8 can define growth 
First, I think the documentation is misleading, I would consider growth to be

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 sigma2_vdelta_8/sigma_8**2 
Second, I couldn't figure out what "fluid" was being used here. Is this CMB+baryons (fluid=8), or does it include neutrinos (fluid=8)? I guess whenever we have massive neutrinos, "f" becomes ill-defined, and one should use f(z,k). Is there a standard / efficient way to compute f(z,k), specifying a particular fluid?

Thanks,
Andreu

Antony Lewis
Posts: 1652
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: CAMB: computing logarithmic growth rate "f"

You can more directly use

(the other doc string should say "growth parameter f*sigma_8"). By default it is using config.transfer_power_var (defaults to baryons+CDM+neutrinos) and the CDM velocity. More generally you can use
with whatever variables you like.

However, in general it may be best to try to calculate the actual physical quantity being measured rather some rather ill-defined growth parameter.

For mode evolution you can use
or use the general matter power spectrum at specific requested redshifts

Andreu Font-Ribera
Posts: 2
Joined: October 17 2016
Affiliation: UCL

### Re: CAMB: computing logarithmic growth rate "f"

Thanks, I'll take a look at it and report back.

Cheers,
Andreu

Maria Berti
Posts: 1
Joined: October 26 2020
Affiliation: SISSA - Trieste

### Re: CAMB: computing logarithmic growth rate "f"

Hi!

I'd like to compute f_sigma8, but I need to use the fortran CAMB and not the python wrapper. It is a bit unclear to me how to compute it from the fortran CAMB output. Is there an already implemented way?

I would like also to have e.g. H(z) and the angular distance, as I see it's done in the demo Jupyter notebook.

Thanks!
Maria

Antony Lewis
Posts: 1652
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: CAMB: computing logarithmic growth rate "f"

There are mostly analogous CAMBdata class methods in the fortran.
You can check the python/fortran source for the python functions to see how it's done there.

Saisandri Saini
Posts: 3
Joined: February 13 2020
Affiliation: MHRD

### Re: CAMB: computing logarithmic growth rate "f"

Hi
I have installed latest version of camb. I would like to modify it with Modechord. For this I have made changes to initialpower.f90,result.f90 and camb.f90 according to modified P(k) in Modechord and I have also copied the fortran files of these modules like module modpkparams, access_modpk etc., which were used in above modifications into fortran directory of CAMB.
I have added extra files (modpk, modpk_module etc.) of Modechord to the SOURCEFILE of makefile_main.
Now when I am giving make command in the fortran directory of CAMB then it is showing errors. Kindly help me.

Thanks
Saisandri