## CAMB: modify DM and radiation evolution equation and perturbation equation

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
Zhu-Yao Wang
Posts: 15
Joined: September 16 2020
Affiliation: Northeastern University

### CAMB: modify DM and radiation evolution equation and perturbation equation

Hi all,
I'm trying to add new variables to CAMB but failed to find where should I modify DM and radiation evolution equation and perturbation equation in equations.f90 file after going through the codes for several days.
I would like to know:
1. Where could I modify the evolution of \rho_{DM}? Also \rho_{radiation}?
2. What synchronous equation is used for DM in equations.f90 and where it is located?

Thank you so much for your help!

Antony Lewis
Posts: 1685
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: CAMB: modify DM and radiation evolution equation and perturbation equation

The equations are described in the CAMB notes
https://cosmologist.info/notes/CAMB.pdf

The background CDM density (grhoc) is just obtained from the usual $\propto 1/a^3$ scaling. The perturbation variable is "clxc".