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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.
# ==============================================================================
"""Version 2 of class Optimizer."""
# pylint: disable=g-bad-name
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from tensorflow.python.keras.optimizer_v2 import optimizer_v2
from tensorflow.python.util import deprecation
class OptimizerV2(optimizer_v2.OptimizerV2):
"""Updated base class for optimizers.
This class defines the API to add Ops to train a model. You never use this
class directly, but instead instantiate one of its subclasses such as
`GradientDescentOptimizer`, `AdagradOptimizer`, or `MomentumOptimizer`.
### Usage
```python
# Create an optimizer with the desired parameters.
opt = GradientDescentOptimizer(learning_rate=0.1)
# Add Ops to the graph to minimize a cost by updating a list of variables.
# "cost" is a Tensor, and the list of variables contains tf.Variable
# objects.
opt_op = opt.minimize(cost, var_list=<list of variables>)
```
In the training program you will just have to run the returned Op.
```python
# Execute opt_op to do one step of training:
opt_op.run()
```
### Processing gradients before applying them.
Calling `minimize()` takes care of both computing the gradients and
applying them to the variables. If you want to process the gradients
before applying them you can instead use the optimizer in three steps:
1. Compute the gradients with `compute_gradients()`.
2. Process the gradients as you wish.
3. Apply the processed gradients with `apply_gradients()`.
Example:
```python
# Create an optimizer.
opt = GradientDescentOptimizer(learning_rate=0.1)
# Compute the gradients for a list of variables.
grads_and_vars = opt.compute_gradients(loss, <list of variables>)
# grads_and_vars is a list of tuples (gradient, variable). Do whatever you
# need to the 'gradient' part, for example cap them, etc.
capped_grads_and_vars = [(MyCapper(gv[0]), gv[1]) for gv in grads_and_vars]
# Ask the optimizer to apply the capped gradients.
opt.apply_gradients(capped_grads_and_vars)
```
### Gating Gradients
Both `minimize()` and `compute_gradients()` accept a `gate_gradients`
argument that controls the degree of parallelism during the application of
the gradients.
The possible values are: `GATE_NONE`, `GATE_OP`, and `GATE_GRAPH`.
<b>`GATE_NONE`</b>: Compute and apply gradients in parallel. This provides
the maximum parallelism in execution, at the cost of some non-reproducibility
in the results. For example the two gradients of `matmul` depend on the input
values: With `GATE_NONE` one of the gradients could be applied to one of the
inputs _before_ the other gradient is computed resulting in non-reproducible
results.
<b>`GATE_OP`</b>: For each Op, make sure all gradients are computed before
they are used. This prevents race conditions for Ops that generate gradients
for multiple inputs where the gradients depend on the inputs.
<b>`GATE_GRAPH`</b>: Make sure all gradients for all variables are computed
before any one of them is used. This provides the least parallelism but can
be useful if you want to process all gradients before applying any of them.
### Slots
Some optimizer subclasses, such as `MomentumOptimizer` and `AdagradOptimizer`
allocate and manage additional variables associated with the variables to
train. These are called <i>Slots</i>. Slots have names and you can ask the
optimizer for the names of the slots that it uses. Once you have a slot name
you can ask the optimizer for the variable it created to hold the slot value.
This can be useful if you want to log debug a training algorithm, report stats
about the slots, etc.
### Non-slot variables
Some optimizer subclasses, such as `AdamOptimizer` have variables that
are not associated with the variables to train, just the step itself.
### Hyper parameters
These are arguments passed to the optimizer subclass constructor
(the `__init__` method), and then passed to `self._set_hyper()`.
They can be either regular Python values (like 1.0), tensors, or
callables. If they are callable, the callable will be called during
`apply_gradients()` to get the value for the hyper parameter.
### State
Internal methods are passed a `state` argument with the correct
values to use for the slot and non-slot variables, and the hyper
parameters.
"""
# Values for gate_gradients.
GATE_NONE = 0
GATE_OP = 1
GATE_GRAPH = 2
@deprecation.deprecated_args(
"2018-10-01",
"`use_locking = True` is no longer supported and will be ignored.",
("use_locking", [False]))
def __init__(self, use_locking, name):
"""Create a new Optimizer.
This must be called by the constructors of subclasses.
Note that Optimizer instances should not bind to a single graph,
and so shouldn't keep Tensors as member variables. Generally
you should be able to use the _set_hyper()/state.get_hyper()
facility instead.
Args:
use_locking: Bool. If True apply use locks to prevent concurrent updates
to variables.
name: A non-empty string. The name to use for accumulators created
for the optimizer.
Raises:
ValueError: If name is malformed.
RuntimeError: If _create_slots has been overridden instead of
_create_vars.
"""
super(OptimizerV2, self).__init__(name)
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