## CosmoMC: Adding w0/wa as fitting parameters

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

### CosmoMC: Adding w0/wa as fitting parameters

Hi,

I'm trying to reproduce Fig. 27 on page 39 of Planck Collaboration XIII (http://arxiv.org/pdf/1502.01589v2.pdf). My first attempt was to use equations_ppf.f90 instead of equations.f90 in CAMB, but I think that just means that the underlying cosmology has a PPF dark energy model, but doesn't add w0 and wa as fitting parameters?

What I then need is to add w0 and wa as fitting parameters to the chains produced by CosmoMC, and my current attempts at this has so far failed. The older threads on this topic seem to not be valid for the version of CosmoMC I'm using (July 2015), and I couldn't find the answer in the ReadMe documentation either.

I'm sure it's possible, and I would greatly appreciate it if someone could provide an answer or point me in the direction of one.

Thank you!
- Per

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

### Re: CosmoMC: Adding w0/wa as fitting parameters

w and wa are available when you do a default build of CosmoMC (which uses equations_ppf.f90).

Per Andersen
Posts: 3
Joined: November 17 2015
Affiliation: University of Copenhagen

### CosmoMC: Adding w0/wa as fitting parameters

Just for future reference, if anyone else find themselves in the same situation I was in all you have to do is go to the directory

Code: Select all

/cosmomc/batch2/
and edit the file params_CMB_defaults.ini and set e.g.

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param&#91;wa&#93; = 0
to five numbers that represent center, min, max, start width, propose width. It's explained in the comments of the file fairly well.

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

### Re: CosmoMC: Adding w0/wa as fitting parameters

Or, better, define param[wa] in your main .ini file which includes from params_CMB_defaults.ini (like test_planck.ini), so you don't change batch2.