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- # coding=utf-8
- # Copyright 2018 The Google AI Language Team Authors.
- #
- # Licensed under the Apache License, Version 2.0 (the "License");
- # you may not use this file except in compliance with the License.
- # You may obtain a copy of the License at
- #
- # http://www.apache.org/licenses/LICENSE-2.0
- #
- # Unless required by applicable law or agreed to in writing, software
- # distributed under the License is distributed on an "AS IS" BASIS,
- # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- # See the License for the specific language governing permissions and
- # limitations under the License.
- """Functions and classes related to optimization (weight updates)."""
- from __future__ import absolute_import
- from __future__ import division
- from __future__ import print_function
- import re
- import tensorflow as tf
- def create_optimizer(loss, init_lr, num_train_steps, num_warmup_steps, use_tpu):
- """Creates an optimizer training op."""
- global_step = tf.train.get_or_create_global_step()
- learning_rate = tf.constant(value=init_lr, shape=[], dtype=tf.float32)
- # Implements linear decay of the learning rate.
- learning_rate = tf.train.polynomial_decay(
- learning_rate,
- global_step,
- num_train_steps,
- end_learning_rate=0.0,
- power=1.0,
- cycle=False)
- # Implements linear warmup. I.e., if global_step < num_warmup_steps, the
- # learning rate will be `global_step/num_warmup_steps * init_lr`.
- if num_warmup_steps:
- global_steps_int = tf.cast(global_step, tf.int32)
- warmup_steps_int = tf.constant(num_warmup_steps, dtype=tf.int32)
- global_steps_float = tf.cast(global_steps_int, tf.float32)
- warmup_steps_float = tf.cast(warmup_steps_int, tf.float32)
- warmup_percent_done = global_steps_float / warmup_steps_float
- warmup_learning_rate = init_lr * warmup_percent_done
- is_warmup = tf.cast(global_steps_int < warmup_steps_int, tf.float32)
- learning_rate = (
- (1.0 - is_warmup) * learning_rate + is_warmup * warmup_learning_rate)
- # It is recommended that you use this optimizer for fine tuning, since this
- # is how the model was trained (note that the Adam m/v variables are NOT
- # loaded from init_checkpoint.)
- optimizer = AdamWeightDecayOptimizer(
- learning_rate=learning_rate,
- weight_decay_rate=0.01,
- beta_1=0.9,
- beta_2=0.999,
- epsilon=1e-6,
- exclude_from_weight_decay=["LayerNorm", "layer_norm", "bias"])
- if use_tpu:
- optimizer = tf.contrib.tpu.CrossShardOptimizer(optimizer)
- tvars = tf.trainable_variables()
- grads = tf.gradients(loss, tvars)
- # This is how the model was pre-trained.
- (grads, _) = tf.clip_by_global_norm(grads, clip_norm=1.0)
- train_op = optimizer.apply_gradients(
- zip(grads, tvars), global_step=global_step)
- # Normally the global step update is done inside of `apply_gradients`.
- # However, `AdamWeightDecayOptimizer` doesn't do this. But if you use
- # a different optimizer, you should probably take this line out.
- new_global_step = global_step + 1
- train_op = tf.group(train_op, [global_step.assign(new_global_step)])
- return train_op
- class AdamWeightDecayOptimizer(tf.train.Optimizer):
- """A basic Adam optimizer that includes "correct" L2 weight decay."""
- def __init__(self,
- learning_rate,
- weight_decay_rate=0.0,
- beta_1=0.9,
- beta_2=0.999,
- epsilon=1e-6,
- exclude_from_weight_decay=None,
- name="AdamWeightDecayOptimizer"):
- """Constructs a AdamWeightDecayOptimizer."""
- super(AdamWeightDecayOptimizer, self).__init__(False, name)
- self.learning_rate = learning_rate
- self.weight_decay_rate = weight_decay_rate
- self.beta_1 = beta_1
- self.beta_2 = beta_2
- self.epsilon = epsilon
- self.exclude_from_weight_decay = exclude_from_weight_decay
- def apply_gradients(self, grads_and_vars, global_step=None, name=None):
- """See base class."""
- assignments = []
- for (grad, param) in grads_and_vars:
- if grad is None or param is None:
- continue
- param_name = self._get_variable_name(param.name)
- m = tf.get_variable(
- name=param_name + "/adam_m",
- shape=param.shape.as_list(),
- dtype=tf.float32,
- trainable=False,
- initializer=tf.zeros_initializer())
- v = tf.get_variable(
- name=param_name + "/adam_v",
- shape=param.shape.as_list(),
- dtype=tf.float32,
- trainable=False,
- initializer=tf.zeros_initializer())
- # Standard Adam update.
- next_m = (
- tf.multiply(self.beta_1, m) + tf.multiply(1.0 - self.beta_1, grad))
- next_v = (
- tf.multiply(self.beta_2, v) + tf.multiply(1.0 - self.beta_2,
- tf.square(grad)))
- update = next_m / (tf.sqrt(next_v) + self.epsilon)
- # Just adding the square of the weights to the loss function is *not*
- # the correct way of using L2 regularization/weight decay with Adam,
- # since that will interact with the m and v parameters in strange ways.
- #
- # Instead we want ot decay the weights in a manner that doesn't interact
- # with the m/v parameters. This is equivalent to adding the square
- # of the weights to the loss with plain (non-momentum) SGD.
- if self._do_use_weight_decay(param_name):
- update += self.weight_decay_rate * param
- update_with_lr = self.learning_rate * update
- next_param = param - update_with_lr
- assignments.extend(
- [param.assign(next_param),
- m.assign(next_m),
- v.assign(next_v)])
- return tf.group(*assignments, name=name)
- def _do_use_weight_decay(self, param_name):
- """Whether to use L2 weight decay for `param_name`."""
- if not self.weight_decay_rate:
- return False
- if self.exclude_from_weight_decay:
- for r in self.exclude_from_weight_decay:
- if re.search(r, param_name) is not None:
- return False
- return True
- def _get_variable_name(self, param_name):
- """Get the variable name from the tensor name."""
- m = re.match("^(.*):\\d+$", param_name)
- if m is not None:
- param_name = m.group(1)
- return param_name
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