Getting started - progenax — differentiable initial conditions for N-body simulations

This section is the onboarding path for new progenax users. The progression is short and concrete: install the package, build your first Plummer sphere, take a gradient through it, sample an IMF, and along the way pick up the glossary terms you’ll see throughout the rest of the docs.

Reading order¶

Page	What you’ll do
Science capabilities	Survey what progenax can model (the model inventory with validity regimes)
Installation	Install progenax via UV (preferred) or pip; verify with the smoke test
Your first Plummer sphere	Build a 1000-particle Plummer cluster from scratch in 5 minutes
Taking gradients through an IC	Take `jax.grad` through the IC builder; see HMC inference in action
IMF sampling	Sample masses from Salpeter, Kroupa, Chabrier, Maschberger, and visualise
Glossary	Definitions of every term used in the rest of the docs
What's new	Release-style changelog

Who this section is for¶

Grad students new to differentiable astrophysics. Read in order.
Researchers familiar with N-body codes (NBODY6, COSMIC, McLuster). Skim Installation, then jump to Units policy and Virial Q convention (Q = T/|V|) — those are the convention differences most likely to bite.
Returning users. What's new is the changelog; the rest of this section is for first-time users.

What progenax is¶

progenax generates initial conditions (ICs) for N-body simulations of star clusters, stellar populations, and binary systems. Every IC is fully differentiable through jax.grad, JIT-compilable through jax.jit, and vectorisable through jax.vmap — the four operations that make HMC inference of cluster parameters tractable.

The package is part of the jaxstro ecosystem: progenax for ICs, gravax for N-body integration, fluxax for photometry, with stellax (stellar evolution) and startrax (binary population synthesis) planned.

What progenax is not¶

progenax does not evolve simulations forward in time — that is gravax’s job. The handoff is documented in Interface with gravax. progenax also does not compute mock observations from final snapshots — that is fluxax (fluxax.render; the old gravax.render monolith is legacy).

Next step¶

Open Installation and run the smoke test. The rest of this section assumes a working install.