Initial conditions at 2nd order

[averagecode]

Dear CLASS team

I am trying to extract the initial conditions for the matter perturbations, i would like to have delta, delta-prime and delta-prime-prime at a given redshift. I am struggling to see how to extract this information and if it is even possible. Any help would greatly be appreciated.

Thanks in advance.

[ThomasTram]

Hi. If you ask for density and velocity transfer functions, you can use the get_transfer(z) method. This will give you delta and theta for any species, and they are first order accurate. Various metric transfer functions are also available, and that should allow you to reconstruct what you need.
Cheers,
Thomas

[averagecode]

@ThomasTram Thank you for your response. This helped a lot. I am now having some other issues trying to make sure I actually get the right values for the perturbations out so that I can use them as initial conditions. For the values one obtains from get_transfer() or get_perturbations(), specifically the "delta_cdm" and "d_cdm", are they precisely the values for delta (or the transfer functions) or are they some rescaled value that I need to adjust to get the value I need? (I want to numerically solve for the delta(a)-evolution equation for a modified dark matter model, i.e d''(a)+.d'(a)+...=0 )