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# Copyright 2019 The TensorFlow Authors. All Rights Reserved.
#
# 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.
# ==============================================================================
"""Optimizer from addons and learning rate scheduler."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
import numpy as np
import tensorflow as tf
K = tf.keras.backend
class LearningRateSchedule(tf.keras.optimizers.schedules.LearningRateSchedule):
"""Learning rate schedule."""
def __init__(self, initial_learning_rate, hidden_size, warmup_steps):
"""Initialize configuration of the learning rate schedule.
Args:
initial_learning_rate: A float, the initial learning rate.
hidden_size: An integer, the model dimension in the hidden layers.
warmup_steps: An integer, the number of steps required for linear warmup.
"""
super(LearningRateSchedule, self).__init__()
self.initial_learning_rate = initial_learning_rate
self.hidden_size = hidden_size
self.warmup_steps = tf.cast(warmup_steps, tf.float32)
def __call__(self, global_step):
"""Calculate learning rate with linear warmup and rsqrt decay.
Args:
global_step: An integer, the current global step used for learning rate
calculation.
Returns:
A float, the learning rate needs to be used for current global step.
"""
with tf.name_scope('learning_rate_schedule'):
global_step = tf.cast(global_step, tf.float32)
learning_rate = self.initial_learning_rate
learning_rate *= (self.hidden_size**-0.5)
# Apply linear warmup
learning_rate *= tf.minimum(1.0, global_step / self.warmup_steps)
# Apply rsqrt decay
learning_rate /= tf.sqrt(tf.maximum(global_step, self.warmup_steps))
return learning_rate
def get_config(self):
"""Get the configuration of the learning rate schedule."""
return {
'initial_learning_rate': self.initial_learning_rate,
'hidden_size': self.hidden_size,
'warmup_steps': self.warmup_steps,
}
class LearningRateFn(object):
"""Creates learning rate function."""
def __init__(self, learning_rate, hidden_size, warmup_steps):
self.learning_rate = learning_rate
self.hidden_size = hidden_size
self.warmup_steps = float(warmup_steps)
def __call__(self, global_step):
"""Calculate learning rate with linear warmup and rsqrt decay."""
step = float(global_step)
learning_rate = self.learning_rate
learning_rate *= (self.hidden_size ** -0.5)
# Apply linear warmup
learning_rate *= np.minimum(1.0, step / self.warmup_steps)
# Apply rsqrt decay
learning_rate /= np.sqrt(np.maximum(step, self.warmup_steps))
return learning_rate
class LearningRateScheduler(tf.keras.callbacks.Callback):
"""Keras callback to schedule learning rate.
TODO(tianlin): Refactor this scheduler and LearningRateBatchScheduler in
official/resnet/keras/keras_common.py.
"""
def __init__(self, schedule, init_steps=None, verbose=False):
super(LearningRateScheduler, self).__init__()
self.schedule = schedule
self.verbose = verbose
if init_steps is None:
init_steps = 0.0
self.steps = float(init_steps) # Total steps during training.
def on_epoch_begin(self, epoch, logs=None):
if not hasattr(self.model.optimizer, 'lr'):
raise ValueError('Optimizer must have a "lr" attribute.')
if not hasattr(self.model.optimizer, 'iterations'):
raise ValueError('Optimizer must have a "iterations" attribute.')
def on_train_batch_begin(self, batch, logs=None):
"""Adjusts learning rate for each train batch."""
if self.verbose > 0:
iterations = K.get_value(self.model.optimizer.iterations)
print('Original iteration %d' % iterations)
self.steps += 1.0
try: # new API
lr = float(K.get_value(self.model.optimizer.lr))
lr = self.schedule(self.steps, lr)
except TypeError: # Support for old API for backward compatibility
lr = self.schedule(self.steps)
if not isinstance(lr, (float, np.float32, np.float64)):
raise ValueError('The output of the "schedule" function '
'should be float.')
K.set_value(self.model.optimizer.lr, lr)
K.set_value(self.model.optimizer.iterations, self.steps)
if self.verbose > 0:
print('Batch %05d Step %05d: LearningRateScheduler setting learning '
'rate to %s.' % (batch + 1, self.steps, lr))
def on_epoch_end(self, epoch, logs=None):
logs = logs or {}
logs['lr'] = K.get_value(self.model.optimizer.lr)
logs['steps'] = self.steps
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