Source code for

# Copyright 2022 The Flax Authors.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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# Unless required by applicable law or agreed to in writing, software
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from typing import Any, Callable

from flax import core
from flax import struct
import optax

[docs]class TrainState(struct.PyTreeNode): """Simple train state for the common case with a single Optax optimizer. Synopsis:: state = TrainState.create( apply_fn=model.apply, params=variables['params'], tx=tx) grad_fn = jax.grad(make_loss_fn(state.apply_fn)) for batch in data: grads = grad_fn(state.params, batch) state = state.apply_gradients(grads=grads) Note that you can easily extend this dataclass by subclassing it for storing additional data (e.g. additional variable collections). For more exotic usecases (e.g. multiple optimizers) it's probably best to fork the class and modify it. Args: step: Counter starts at 0 and is incremented by every call to `.apply_gradients()`. apply_fn: Usually set to `model.apply()`. Kept in this dataclass for convenience to have a shorter params list for the `train_step()` function in your training loop. params: The parameters to be updated by `tx` and used by `apply_fn`. tx: An Optax gradient transformation. opt_state: The state for `tx`. """ step: int apply_fn: Callable = struct.field(pytree_node=False) params: core.FrozenDict[str, Any] tx: optax.GradientTransformation = struct.field(pytree_node=False) opt_state: optax.OptState
[docs] def apply_gradients(self, *, grads, **kwargs): """Updates `step`, `params`, `opt_state` and `**kwargs` in return value. Note that internally this function calls `.tx.update()` followed by a call to `optax.apply_updates()` to update `params` and `opt_state`. Args: grads: Gradients that have the same pytree structure as `.params`. **kwargs: Additional dataclass attributes that should be `.replace()`-ed. Returns: An updated instance of `self` with `step` incremented by one, `params` and `opt_state` updated by applying `grads`, and additional attributes replaced as specified by `kwargs`. """ updates, new_opt_state = self.tx.update( grads, self.opt_state, self.params) new_params = optax.apply_updates(self.params, updates) return self.replace( step=self.step + 1, params=new_params, opt_state=new_opt_state, **kwargs, )
[docs] @classmethod def create(cls, *, apply_fn, params, tx, **kwargs): """Creates a new instance with `step=0` and initialized `opt_state`.""" opt_state = tx.init(params) return cls( step=0, apply_fn=apply_fn, params=params, tx=tx, opt_state=opt_state, **kwargs, )