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 CAMB: calculating derivatives of Cl's wrt parameters
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Joined: 17 Jul 2014
Posts: 16
Affiliation: Johns Hopkins University

 Posted: 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 $\frac{\partial C_{\ell}}{\partial(\Omega_ch^2)}$ 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

Joined: 23 Sep 2004
Posts: 1303
Affiliation: University of Sussex

 Posted: August 09 2017 That's usually the best way. (unless you really want parameter errors/forecasts - in which case run CosmoMC).

Joined: 17 Jul 2014
Posts: 16
Affiliation: Johns Hopkins University

 Posted: 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

Joined: 23 Sep 2004
Posts: 1303
Affiliation: University of Sussex

 Posted: August 10 2017 You probably could, but it might take some thought on how to code it.

Joined: 17 Jul 2014
Posts: 16
Affiliation: Johns Hopkins University

 Posted: 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.
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