JAX Scientific Computing

Core Rules

1. Pure functions - No side effects
2. JIT outer functions - @jax.jit on hot paths
3. vmap not loops - jax.vmap(fn) instead of list comprehensions
4. Split RNG keys - Never reuse keys

Patterns

# RNG: always split
key, k1, k2 = jax.random.split(key, 3)

# Batching: vmap not loops
batched = jax.vmap(fn)(inputs)

# Loops: use scan
_, results = jax.lax.scan(step_fn, init, xs)

Gotchas

• Arrays are immutable
• No Python control flow in JIT - use jax.lax.cond, jax.lax.scan
• Check NaNs: jnp.isnan(x).any()