## CAMB: equations_PPF.f90 question

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Per Andersen
Posts: 3
Joined: November 17 2015
Affiliation: University of Copenhagen

### CAMB: equations_PPF.f90 question

Hi,

I'm working on a project where I need to modify the parameterisation w(a) = w0 + wa * (1-a) from the equations_PPF.f90 file used in CAMB and CosmoMC.

I can tell that I definitely need to modify line 98:

Code: Select all

w_de=w_lam+wa_ppf*&#40;1._dl-a&#41;
But then in line 143 we have:

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grho_de=grhov*a**&#40;1._dl-3.*w_lam-3.*wa_ppf&#41;*exp&#40;-3.*wa_ppf*&#40;1._dl-a&#41;&#41;
I'm unsure exactly what this equation is. To me it looks very close to the behaviour of dark energy density which is:

Code: Select all

f&#40;a&#41; = a**&#40;-3.*&#40;1+w_lam+wa_ppf&#41;&#41; * exp&#40;-3*wa_ppf*&#40;1.-a&#41;&#41;
(See e.g. Appendix A of King 2014, http://arxiv.org/abs/1311.2356)

So, in summary - what role does line 143 of equations_PPF.f90 play in CAMB, and if I want to modify the w(a) = w0 + wa * (1-a) parameterisation do I also need to modify line 143 and not just line 98?

Thank you!
- Per

Antony Lewis
Posts: 1636
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: CAMB: equations_PPF.f90 question

Yes. grho_de(a) returns $8 \pi G a^4\rho_{de}$.