Equinox

Equinox is a JAX library for parameterised functions (e.g. neural networks) offering:

• a PyTorch-like API...
• ...that's fully compatible with native JAX transformations...
• ...with no new concepts you have to learn.

If you're completely new to JAX, then start with this CNN on MNIST example.
If you're already familiar with JAX, then the main idea is to represent parameterised functions (such as neural networks) as PyTrees, so that they can pass across JIT/grad/etc. boundaries smoothly.

The elegance of Equinox is its selling point in a world that already has Haiku, Flax and so on.

In other words, why should you care? Because Equinox is really simple to learn, and really simple to use.

Installation

pip install equinox

Requires Python 3.9+ and JAX 0.4.11+.

Documentation

Available at https://docs.kidger.site/equinox.

Quick example

Models are defined using PyTorch-like syntax:

import equinox as eqx
import jax

class Linear(eqx.Module):
    weight: jax.Array
    bias: jax.Array

    def __init__(self, in_size, out_size, key):
        wkey, bkey = jax.random.split(key)
        self.weight = jax.random.normal(wkey, (out_size, in_size))
        self.bias = jax.random.normal(bkey, (out_size,))

    def __call__(self, x):
        return self.weight @ x + self.bias

and fully compatible with normal JAX operations:

@jax.jit
@jax.grad
def loss_fn(model, x, y):
    pred_y = jax.vmap(model)(x)
    return jax.numpy.mean((y - pred_y) ** 2)

batch_size, in_size, out_size = 32, 2, 3
model = Linear(in_size, out_size, key=jax.random.PRNGKey(0))
x = jax.numpy.zeros((batch_size, in_size))
y = jax.numpy.zeros((batch_size, out_size))
grads = loss_fn(model, x, y)

Finally, there's no magic behind the scenes. All eqx.Module does is register your class as a PyTree. From that point onwards, JAX already knows how to work with PyTrees.

Citation

If you found this library to be useful in academic work, then please cite: (arXiv link)

@article{kidger2021equinox,
    author={Patrick Kidger and Cristian Garcia},
    title={{E}quinox: neural networks in {JAX} via callable {P}y{T}rees and filtered transformations},
    year={2021},
    journal={Differentiable Programming workshop at Neural Information Processing Systems 2021}
}

(Also consider starring the project on GitHub.)

See also: other libraries in the JAX ecosystem

Optax: first-order gradient (SGD, Adam, ...) optimisers.

Diffrax: numerical differential equation solvers.

Lineax: linear solvers and linear least squares.

jaxtyping: type annotations for shape/dtype of arrays.

Eqxvision: computer vision models.

sympy2jax: SymPy<->JAX conversion; train symbolic expressions via gradient descent.