Neural Nets for JAX
JAXnet is a deep learning library based on JAX. JAXnet's functional API provides unique benefits over TensorFlow2, Keras and PyTorch, while maintaining user-friendliness, modularity and scalability:
- More robustness through immutable weights, no global compute graph.
numpycode for networks, training loops, pre- and postprocessing.
- Regularization and reparametrization of any module or whole networks in one line.
- No global random state, flexible random key control.
If you already know stax, read this.
net = Sequential(Dense(1024), relu, Dense(1024), relu, Dense(4), log_softmax)
creates a neural net model from predefined modules.
Define your own modules using
@parametrized functions. You can reuse other modules:
from jax import numpy as jnp @parametrized def loss(inputs, targets): return -jnp.mean(net(inputs) * targets)
All modules are composed in this way.
jax.numpy is mirroring
meaning that if you know how to use
numpy, you know most of JAXnet.
Compare this to TensorFlow2/Keras:
import tensorflow as tf from tensorflow.keras import Sequential from tensorflow.keras.layers import Dense, Lambda net = Sequential([Dense(1024, 'relu'), Dense(1024, 'relu'), Dense(4), Lambda(tf.nn.log_softmax)]) def loss(inputs, targets): return -tf.reduce_mean(net(inputs) * targets)
Lambda layers are not needed in JAXnet.
logsoftmax are plain Python functions.
Different from TensorFlow2/Keras, JAXnet has no global compute graph.
loss do not contain mutable weights.
Instead, weights are contained in separate, immutable objects.
They are initialized with
init_parameters, provided example inputs and a random key:
from jax.random import PRNGKey def next_batch(): return jnp.zeros((3, 784)), jnp.zeros((3, 4)) params = loss.init_parameters(*next_batch(), key=PRNGKey(0)) print(params.sequential.dense2.bias) # [-0.01101029, -0.00749435, -0.00952365, 0.00493979]
Instead of mutating weights inline, optimizers return updated versions of weights.
They are returned as part of a new optimizer state, and can be retrieved via
opt = optimizers.Adam() state = opt.init(params) for _ in range(10): state = opt.update(loss.apply, state, *next_batch()) # accelerate with jit=True trained_params = opt.get_parameters(state)
apply evaluates a network:
test_loss = loss.apply(trained_params, *test_batch) # accelerate with jit=True
GPU support and compilation
JAX allows functional
scipy code to be accelerated.
Make it run on GPU by replacing your
numpy import with
Compile a function by decorating it with
This will free your function from slow Python interpretation, parallelize operations where possible and optimize your compute graph.
It provides speed and scalability at the level of TensorFlow2 or PyTorch.
Due to immutable weights, whole training loops can be compiled / run on GPU (demo).
jit will make your training as fast as mutating weights inline, and weights will not leave the GPU.
You can write functional code without worrying about performance.
You can easily accelerate
scipy pre-/postprocessing code in the same way (demo).
Regularization and reparametrization
In JAXnet, regularizing a model can be done in one line (demo):
loss = L2Regularized(loss, scale=.1)
loss is now just another module that can be used as above.
Reparametrized layers are one-liners, too (see API).
JAXnet allows regularizing or reparametrizing any module or subnetwork without changing its code.
This is possible because modules do not instantiate any variables.
Instead each module provides a function (
apply) with parameters as an argument.
This function can be wrapped to build layers like
In contrast, TensorFlow2/Keras/PyTorch have mutable variables baked into their model API. They therefore require:
- Regularization arguments on layer level, with separate code necessary for each layer.
- Reparametrization arguments on layer level, and separate implementations for each layer.
Random key control
JAXnet does not have global random state. Random keys are provided explicitly, making code deterministic and independent of previously executed code by default. This can help debugging and is more flexible (demo). Read more on random numbers in JAX here.
JAXnet allows step-by-step debugging with concrete values like any plain Python function
jit compilation is not used).
API and demos
Find more details on the API here.
This is a preview. Expect breaking changes! Python 3.6 or higher is supported. Install with
pip3 install jaxnet
To use GPU, first install the right version of jaxlib.
Please feel free to create an issue on GitHub.
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