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Integrating the Sympy-based Boltzmann solver from PyCosmo

See original GitHub issue

Following a very nice talk from Beatrice Moser, I looked a little bit at how PyCosmo is implementing their own Boltzmann code and it’s actually pretty nice and could be pretty easily ported to JAX I think.

The ODE is specificied using Sympy, which makes it pretty easy to write down the equations, and then they use their own sympy2c code to transform the python code into JIT compiled code to run the actual ODE solver.

So that’s pretty cool 😃 But we could make it way cooler by doing the following:

  • Copy/Paste the Sympy equations from PyCosmo (which is GPL licensed)
  • Use Miles’ sympy2jax library to turn the equations into JAX functions
  • Use jax.experimental.odeint to integrate in time the system
  • Profit!

And boom! You got yourself a diffable Boltzman solver!

Issue Analytics

  • State:open
  • Created 2 years ago
  • Comments:5 (3 by maintainers)

github_iconTop GitHub Comments

EiffLcommented, Jan 31, 2022

Also I’m thinking it would be worthwhile to host a JAX Boltzmann solver as a separate project, as opposed to integrating it directly into jax-cosmo.

moserb94commented, Feb 2, 2022

The idea was to use hyrec-2 the way we use RecFast++ (meaning a python wrapper and an interpolator), rather than rewriting the code in sympy… so that wouldn’t help I guess.

Read more comments on GitHub >

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