CosmoCoffee

I am running Planck + BAO data likelihood with the LCDM model in MontePython. I forgot to add H0 and sigma8 as derived parameters in the MontePython param file. How can I add them as a derived parameter in GetDist or is there any other way to obtain them without running the chains again?

My MCMC parameters in the param file are the following:
omega_b, omega_cdm, 100*theta_s, ln10^{10}A_s, n_s, tau_reio

Thanks.

GetDist doesn't know anything about cosmology, so you'd have to compute the sigma8 values externally, e.g. by looping over the chain parameters and computing it.

Cobaya could do this by importance sampling original chains, but I don't know about MontePython.

Thanks, Anthony. I wondered if there is a way to add H0 and sigma8 as Derived Parameters in GetDist when analyzing the chains. Do you think there is a way to do this?

Yes, but you'd need to compute signa8 in an external loop using a cosmology code. The example notebook shows hot to add derived parameters.

Ahhh...I see. I understand. The idea is to run the parameters in the chains (each line of each chain) with CLASS to determine sigma8 and H0. Thanks a bunch.