CosmoCoffee

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

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

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

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