### [CAMB] $N_{eff}$ and taking derivatives

Posted:

**October 07 2018**Hello Dr. Lewis,

I'm interested in taking derivatives of matter power spectra with respect to $N_{eff}$ in order to get Fisher estimates.

Unfortunately, I'm confused because there seem to be two parameters with very similar names, nnu and standard_neutrino_neff.

The documentation has this to say about them:

Furthermore, if I wanted to slightly change $N_{eff}$, I'm unclear as to whether they should both change or only one of them.

I appreciate any assistance.

Felipe Maldonado

I'm interested in taking derivatives of matter power spectra with respect to $N_{eff}$ in order to get Fisher estimates.

Unfortunately, I'm confused because there seem to be two parameters with very similar names, nnu and standard_neutrino_neff.

The documentation has this to say about them:

I apologize, but I'm just uncertain on what is the difference between these two parameters.

nnu– N_eff, effective relativistic degrees of freedom

standard_neutrino_neff– default value for N_eff in standard cosmology (non-integer to allow for partial heating of neutrinos at electron-positron annihilation and QED effects)

Furthermore, if I wanted to slightly change $N_{eff}$, I'm unclear as to whether they should both change or only one of them.

I appreciate any assistance.

Felipe Maldonado