CAMB: calculating derivatives of Cl's wrt parameters

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
Post Reply
Graeme Addison
Posts: 18
Joined: July 17 2014
Affiliation: Johns Hopkins University

CAMB: calculating derivatives of Cl''s wrt parameters

Post by Graeme Addison » August 08 2017

Is there any way to have CAMB calculate derivatives of CMB power spectra with respect to cosmological parameters? I.e. quantities like [tex]\frac{\partial C_{\ell}}{\partial(\Omega_ch^2)}[/tex]

I can numerically estimate derivatives by perturbing parameters and re-running but wanted to check if there's some better / more efficient way.

Thanks

Antony Lewis
Posts: 1361
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: CAMB: calculating derivatives of Cl''''s wrt parameters

Post by Antony Lewis » August 09 2017

That's usually the best way. (unless you really want parameter errors/forecasts - in which case run CosmoMC).

Graeme Addison
Posts: 18
Joined: July 17 2014
Affiliation: Johns Hopkins University

CAMB: calculating derivatives of Cl''s wrt parameters

Post by Graeme Addison » August 10 2017

OK. How about if I want to evaluate these derivatives at each step of a CosmoMC chain? Can I have CAMB called multiple times at each step with slightly different parameters?

Antony Lewis
Posts: 1361
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: CAMB: calculating derivatives of Cl''''s wrt parameters

Post by Antony Lewis » August 10 2017

You probably could, but it might take some thought on how to code it.

Graeme Addison
Posts: 18
Joined: July 17 2014
Affiliation: Johns Hopkins University

CAMB: calculating derivatives of Cl''s wrt parameters

Post by Graeme Addison » August 10 2017

Hmm OK. I think I'll start with figuring out how much the derivatives are really varying in case I don't need to do the recalculation each step. Thanks.

Post Reply