## External power spectrum in cosmomc

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Jack Sparrow
Posts: 14
Joined: May 12 2016
Affiliation: HK

### External power spectrum in cosmomc

Recently, I am trying to work out some parameter constraints on my model. I need to input the power spectrum into cosmomc. The power spectrum has some parameters which can determine the shape. I donâ€™t know how to input the function of power spectrum and then constrain the value of parameters. I know in monte python, there is a file external_Pk which can do this. So, how about cosmomc?

Another question is how to fix the value of parameters in cosmomc,especially the nuisance parameters?

Thanks!

Antony Lewis
Posts: 1407
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: External power spectrum in cosmomc

You need to write your own power spectrum module to replace power_tilt.f90 in CAMB. If it has the same numbers of parameters as the standard model, you can probably just reinterpret ns, nrun, etc as your new parameters and just use them from CosmoMC as normal. Otherwise you'll need to modify Cosmomc to propagate your parameters in the same way that ns, nrun etc are at the moment.

You can use

Code: Select all

param&#91;name&#93;= x

in the .ini file to fix parameter named name to the value x.

Jack Sparrow
Posts: 14
Joined: May 12 2016
Affiliation: HK

### External power spectrum in cosmomc

Thank you very much!

Since I am new to cosmomc and also fortran, could you please tell me more details on how to make relevant changes in cosmomc?

Thanks a lot!

Antony Lewis
Posts: 1407
Joined: September 23 2004
Affiliation: University of Sussex
Contact: