Using CosmoMC with PPF module and usew0wa=F

[Sunny Vagnozzi]

Dear Antony,

apologies for what might be a trivial question...

I am trying to use CosmoMC to get constraints on cosmological parameters in the presence of dark energy with a certain equation of state evolving with redshift/scale factor w(a). So in camb/params.ini I set
usew0wa = F
and then supply a file wa.dat with 2 columns: a=1/(1+z), and w(a)

My question is whether CosmoMC supports this type of user-provided dark energy equation of state? I recall reading in this post http://cosmocoffee.info/viewtopic.php?t ... 1bfb015f9f that CosmoMC does not support tabulated w(a) so I was wondering how to get around this

Cheers,
Sunny

[Antony Lewis]

Yes, that's not supported by default - you'd need to modify it to do that.

[Sunny Vagnozzi]

Dear Antony,

thanks for your reply. I was wondering whether for implementing more complicated equations of state, assuming I have an analytical expression for w(z) which might or might not depend on other cosmological parameters as well (e.g. in models where neutrinos are playing a role in the late-time acceleration?), it is possible to modify lines 97-98 in camb/equations_ppf.f90, which read
if(.not. use_tabulated_w) then
w_de=w_lam+wa_ppf*(1._dl-a)


Assuming I want to implement a parametrization with more than two parameters, would I have to make additional changes to the code, and where?

Cheers,
Sunny

[Antony Lewis]

Yes, something like that should work. If it's quintessence you might want to use equations.f90 rather than the ppf approximation.

For adding parameters see the FAQ answer:
http://cosmologist.info/cosmomc/readme.html#FAQ