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# Copyright 2015 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.
# ==============================================================================
"""Momentum for TensorFlow."""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from tensorflow.python.framework import ops
from tensorflow.python.ops import math_ops
from tensorflow.python.training import optimizer
from tensorflow.python.training import training_ops
from tensorflow.python.util.tf_export import tf_export
@tf_export("train.MomentumOptimizer")
class MomentumOptimizer(optimizer.Optimizer):
"""Optimizer that implements the Momentum algorithm.
Computes (if `use_nesterov = False`):
```
accumulation = momentum * accumulation + gradient
variable -= learning_rate * accumulation
```
Note that in the dense version of this algorithm, `accumulation` is updated
and applied regardless of a gradient's value, whereas the sparse version (when
the gradient is an `IndexedSlices`, typically because of `tf.gather` or an
embedding) only updates variable slices and corresponding `accumulation` terms
when that part of the variable was used in the forward pass.
"""
def __init__(self, learning_rate, momentum,
use_locking=False, name="Momentum", use_nesterov=False):
"""Construct a new Momentum optimizer.
Args:
learning_rate: A `Tensor` or a floating point value. The learning rate.
momentum: A `Tensor` or a floating point value. The momentum.
use_locking: If `True` use locks for update operations.
name: Optional name prefix for the operations created when applying
gradients. Defaults to "Momentum".
use_nesterov: If `True` use Nesterov Momentum.
See [Sutskever et al., 2013](
http://jmlr.org/proceedings/papers/v28/sutskever13.pdf).
This implementation always computes gradients at the value of the
variable(s) passed to the optimizer. Using Nesterov Momentum makes the
variable(s) track the values called `theta_t + mu*v_t` in the paper.
@compatibility(eager)
When eager execution is enabled, `learning_rate` and `momentum` can each be
a callable that takes no arguments and returns the actual value to use. This
can be useful for changing these values across different invocations of
optimizer functions.
@end_compatibility
"""
super(MomentumOptimizer, self).__init__(use_locking, name)
self._learning_rate = learning_rate
self._momentum = momentum
self._use_nesterov = use_nesterov
def _create_slots(self, var_list):
for v in var_list:
self._zeros_slot(v, "momentum", self._name)
def _prepare(self):
learning_rate = self._learning_rate
if callable(learning_rate):
learning_rate = learning_rate()
self._learning_rate_tensor = ops.convert_to_tensor(learning_rate,
name="learning_rate")
momentum = self._momentum
if callable(momentum):
momentum = momentum()
self._momentum_tensor = ops.convert_to_tensor(momentum, name="momentum")
def _apply_dense(self, grad, var):
mom = self.get_slot(var, "momentum")
return training_ops.apply_momentum(
var, mom,
math_ops.cast(self._learning_rate_tensor, var.dtype.base_dtype),
grad,
math_ops.cast(self._momentum_tensor, var.dtype.base_dtype),
use_locking=self._use_locking,
use_nesterov=self._use_nesterov).op
def _resource_apply_dense(self, grad, var):
mom = self.get_slot(var, "momentum")
return training_ops.resource_apply_momentum(
var.handle, mom.handle,
math_ops.cast(self._learning_rate_tensor, grad.dtype.base_dtype),
grad,
math_ops.cast(self._momentum_tensor, grad.dtype.base_dtype),
use_locking=self._use_locking,
use_nesterov=self._use_nesterov)
def _apply_sparse(self, grad, var):
mom = self.get_slot(var, "momentum")
return training_ops.sparse_apply_momentum(
var, mom,
math_ops.cast(self._learning_rate_tensor, var.dtype.base_dtype),
grad.values, grad.indices,
math_ops.cast(self._momentum_tensor, var.dtype.base_dtype),
use_locking=self._use_locking,
use_nesterov=self._use_nesterov).op
def _resource_apply_sparse(self, grad, var, indices):
mom = self.get_slot(var, "momentum")
return training_ops.resource_sparse_apply_momentum(
var.handle, mom.handle,
math_ops.cast(self._learning_rate_tensor, grad.dtype),
grad, indices,
math_ops.cast(self._momentum_tensor, grad.dtype),
use_locking=self._use_locking,
use_nesterov=self._use_nesterov)
|
