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CAMB: calculating derivatives of Cl''s wrt parameters

Posted: August 08 2017
by Graeme Addison
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

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

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

CAMB: calculating derivatives of Cl''s wrt parameters

Posted: August 10 2017
by Graeme Addison
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?

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

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

CAMB: calculating derivatives of Cl''s wrt parameters

Posted: August 10 2017
by Graeme Addison
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.