Fluid with varying w(a)

[akshay-ghalsasi]

I am attempting to implement a fluid with varying equation of state, "w(a)" in CLASS keeping track of its perturbations. There is a generalized fluid module in CLASS which admits a varying w(a). However that seems to apply only to fluids which can be written as ''generalized dark matter" (GDM) model similar to Hu https://arxiv.org/pdf/astro-ph/9801234.pdf or Ballesteros and Lesgourgues https://arxiv.org/pdf/1004.5509.pdf. I have checked and I can't generically express my perturbation equations as a generalized dark matter as assumed by the implementation in CLASS.

Moreover in the part of the fluid evolution where it can be expressed as GDM it dosen't give the expected results I get from my own calculations and from other references I found. The matter power spectrum also seems to be gauge dependent (it changes based on if I select synchronous or Newtonian gauge).

I can provide more details about my model if needed, I kept it brief for readability. I will try to implement my own species in CLASS but before that I have 2 questions.

1 )Is there a CLASS implementation that lets me reproduce a fluid for varying w(a)?

2. I found lecture notes from Tokyo 2014 that walk me through the procedures. Are there any more recent lecture notes? There seem to be some changes to CLASS code since then.

Appreciate any help