# 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.

# ==============================================================================

"""Base class for optimizers."""

# pylint: disable=g-bad-name

from __future__ import absolute_import

from __future__ import division

from __future__ import print_function

import abc

import six

from tensorflow.python.distribute import distribution_strategy_context as distribute_ctx

from tensorflow.python.distribute import reduce_util as ds_reduce_util

from tensorflow.python.eager import backprop

from tensorflow.python.eager import context

from tensorflow.python.framework import dtypes

from tensorflow.python.framework import ops

from tensorflow.python.ops import array_ops

from tensorflow.python.ops import control_flow_ops

from tensorflow.python.ops import gradients

from tensorflow.python.ops import math_ops

from tensorflow.python.ops import resource_variable_ops

from tensorflow.python.ops import state_ops

from tensorflow.python.ops import variable_scope

from tensorflow.python.ops import variables

from tensorflow.python.training import slot_creator

from tensorflow.python.training.tracking import base as trackable

from tensorflow.python.util import nest

from tensorflow.python.util.tf_export import tf_export

def get_filtered_grad_fn(grad_fn):

# `distributed_context.join()` requires that its arguments are parallel

# across threads, and in particular that `grads_and_vars` has the same

# variables in the same order.

# When computing gradients in eager mode with multiple threads, you

# can get extra variables with a gradient of `None`. This happens when

# those variables are accessed in another thread during the gradient

# computation. To get a consistent set of variables, we filter out

# those with `None` gradients.

def filtered_grad_fn(*args, **kwargs):

return [(g, v) for g, v in grad_fn(*args, **kwargs) if g is not None]

return filtered_grad_fn

def _deduplicate_indexed_slices(values, indices):

"""Sums `values` associated with any non-unique `indices`.

Args:

values: A `Tensor` with rank >= 1.

indices: A one-dimensional integer `Tensor`, indexing into the first

dimension of `values` (as in an IndexedSlices object).

Returns:

A tuple of (`summed_values`, `unique_indices`) where `unique_indices` is a

de-duplicated version of `indices` and `summed_values` contains the sum of

`values` slices associated with each unique index.

"""

unique_indices, new_index_positions = array_ops.unique(indices)

summed_values = math_ops.unsorted_segment_sum(

values, new_index_positions,

array_ops.shape(unique_indices)[0])

return (summed_values, unique_indices)

def _var_key(var):

# TODO(ashankar): Consolidate handling for eager and graph

if hasattr(var, "op"):

return (var.op.graph, var.op.name)

return var._unique_id # pylint: disable=protected-access

@six.add_metaclass(abc.ABCMeta)

class _OptimizableVariable(object):

"""Interface for abstracting over variables in the optimizers."""

@abc.abstractmethod

def target(self):

"""Returns the optimization target for this variable."""

raise NotImplementedError("Calling an abstract method.")

@abc.abstractmethod

def update_op(self, optimizer, g):

"""Returns the update ops for updating the variable."""

raise NotImplementedError("Calling an abstract method.")

class _RefVariableProcessor(_OptimizableVariable):

"""Processor for Variable."""

def __init__(self, v):

self._v = v

def __str__(self):

return "<_RefVariableProcessor(%s)>" % self._v

def target(self):

return self._v._ref() # pylint: disable=protected-access

def update_op(self, optimizer, g):

if isinstance(g, ops.Tensor):

update_op = optimizer._apply_dense(g, self._v) # pylint: disable=protected-access

if self._v.constraint is not None:

with ops.control_dependencies([update_op]):

return self._v.assign(self._v.constraint(self._v))

else:

return update_op

else:

assert isinstance(g, ops.IndexedSlices), ("Gradient ", g, " is neither a "

"tensor nor IndexedSlices.")

if self._v.constraint is not None:

raise RuntimeError(

"Cannot use a constraint function on a sparse variable.")

# pylint: disable=protected-access

return optimizer._apply_sparse_duplicate_indices(g, self._v)

class _DenseReadResourceVariableProcessor(_OptimizableVariable):

"""Processor for dense ResourceVariables."""

def __init__(self, v):

self._v = v

def target(self):

return self._v

def update_op(self, optimizer, g):

# pylint: disable=protected-access

update_op = optimizer._resource_apply_dense(g, self._v.op.inputs[0])

if self._v.constraint is not None:

with ops.control_dependencies([update_op]):

return self._v.assign(self._v.constraint(self._v))

else:

return update_op

class _DenseResourceVariableProcessor(_OptimizableVariable):

"""Processor for dense ResourceVariables."""

def __init__(self, v):

self._v = v

def target(self):

return self._v

def update_op(self, optimizer, g):

# pylint: disable=protected-access

if isinstance(g, ops.IndexedSlices):

if self._v.constraint is not None:

raise RuntimeError(

"Cannot use a constraint function on a sparse variable.")

return optimizer._resource_apply_sparse_duplicate_indices(

g.values, self._v, g.indices)

update_op = optimizer._resource_apply_dense(g, self._v)

if self._v.constraint is not None:

with ops.control_dependencies([update_op]):

return self._v.assign(self._v.constraint(self._v))

else:

return update_op

class _TensorProcessor(_OptimizableVariable):

"""Processor for ordinary Tensors.

Even though a Tensor can't really be updated, sometimes it is useful to

compute the gradients with respect to a Tensor using the optimizer. Updating

the Tensor is, of course, unsupported.

"""

def __init__(self, v):

self._v = v

def target(self):

return self._v

def update_op(self, optimizer, g):

raise NotImplementedError("Trying to update a Tensor ", self._v)

def _get_processor(v):

"""The processor of v."""

if context.executing_eagerly():

if isinstance(v, ops.Tensor):

return _TensorProcessor(v)

else:

return _DenseResourceVariableProcessor(v)

if resource_variable_ops.is_resource_variable(v) and not v._in_graph_mode: # pylint: disable=protected-access

# True if and only if `v` was initialized eagerly.

return _DenseResourceVariableProcessor(v)

if v.op.type == "VarHandleOp":

return _DenseResourceVariableProcessor(v)

if isinstance(v, variables.Variable):

return _RefVariableProcessor(v)

if isinstance(v, ops.Tensor):

return _TensorProcessor(v)

raise NotImplementedError("Trying to optimize unsupported type ", v)

@tf_export(v1=["train.Optimizer"])

class Optimizer(

# Optimizers inherit from Trackable rather than AutoTrackable

# since they do most of their dependency management themselves (slot

# variables are special-cased, and non-slot variables are keyed to graphs).

trackable.Trackable):

"""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.

"""

# Values for gate_gradients.

GATE_NONE = 0

GATE_OP = 1

GATE_GRAPH = 2

def __init__(self, use_locking, name):

"""Create a new Optimizer.

This must be called by the constructors of subclasses.

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.

"""

if not name:

raise ValueError("Must specify the optimizer name")

self._use_locking = use_locking

self._name = name

# Dictionary of slots.

# {slot_name :

# {_var_key(variable_to_train): slot_for_the_variable, ... },

# ... }

self._slots = {}

self._non_slot_dict = {}

# For implementing Trackable. Stores information about how to restore

# slot variables which have not yet been created

# (trackable._CheckpointPosition objects).

# {slot_name :

# {_var_key(variable_to_train): [checkpoint_position, ... ], ... },

# ... }

self._deferred_slot_restorations = {}

# TODO(isaprykin): When using a DistributionStrategy, and when an

# optimizer is created in each replica, it might be dangerous to

# rely on some Optimizer methods. When such methods are called on a

# per-replica optimizer, an exception needs to be thrown. We do

# allow creation per-replica optimizers however, because the

# compute_gradients()->apply_gradients() sequence is safe.

def get_name(self):

return self._name

def minimize(self, loss, global_step=None, var_list=None,

gate_gradients=GATE_OP, aggregation_method=None,

colocate_gradients_with_ops=False, name=None,

grad_loss=None):

"""Add operations to minimize `loss` by updating `var_list`.

This method simply combines calls `compute_gradients()` and

`apply_gradients()`. If you want to process the gradient before applying

them call `compute_gradients()` and `apply_gradients()` explicitly instead

of using this function.

Args:

loss: A `Tensor` containing the value to minimize.

global_step: Optional `Variable` to increment by one after the

variables have been updated.

var_list: Optional list or tuple of `Variable` objects to update to

minimize `loss`. Defaults to the list of variables collected in

the graph under the key `GraphKeys.TRAINABLE_VARIABLES`.

gate_gradients: How to gate the computation of gradients. Can be

`GATE_NONE`, `GATE_OP`, or `GATE_GRAPH`.

aggregation_method: Specifies the method used to combine gradient terms.

Valid values are defined in the class `AggregationMethod`.

colocate_gradients_with_ops: If True, try colocating gradients with

the corresponding op.

name: Optional name for the returned operation.

grad_loss: Optional. A `Tensor` holding the gradient computed for `loss`.

Returns:

An Operation that updates the variables in `var_list`. If `global_step`

was not `None`, that operation also increments `global_step`.

Raises:

ValueError: If some of the variables are not `Variable` objects.

@compatibility(eager)

When eager execution is enabled, `loss` should be a Python function that

takes no arguments and computes the value to be minimized. Minimization (and

gradient computation) is done with respect to the elements of `var_list` if

not None, else with respect to any trainable variables created during the

execution of the `loss` function. `gate_gradients`, `aggregation_method`,

`colocate_gradients_with_ops` and `grad_loss` are ignored when eager

execution is enabled.

@end_compatibility

"""

grads_and_vars = self.compute_gradients(

loss, var_list=var_list, gate_gradients=gate_gradients,

aggregation_method=aggregation_method,

colocate_gradients_with_ops=colocate_gradients_with_ops,

grad_loss=grad_loss)

vars_with_grad = [v for g, v in grads_and_vars if g is not None]

if not vars_with_grad:

raise ValueError(

"No gradients provided for any variable, check your graph for ops"

" that do not support gradients, between variables %s and loss %s." %

([str(v) for _, v in grads_and_vars], loss))

return self.apply_gradients(grads_and_vars, global_step=global_step,

name=name)

def compute_gradients(self, loss, var_list=None,

gate_gradients=GATE_OP,

aggregation_method=None,

colocate_gradients_with_ops=False,

grad_loss=None):

"""Compute gradients of `loss` for the variables in `var_list`.

This is the first part of `minimize()`. It returns a list

of (gradient, variable) pairs where "gradient" is the gradient

for "variable". Note that "gradient" can be a `Tensor`, an

`IndexedSlices`, or `None` if there is no gradient for the

given variable.

Args:

loss: A Tensor containing the value to minimize or a callable taking

no arguments which returns the value to minimize. When eager execution

is enabled it must be a callable.

var_list: Optional list or tuple of `tf.Variable` to update to minimize

`loss`. Defaults to the list of variables collected in the graph

under the key `GraphKeys.TRAINABLE_VARIABLES`.

gate_gradients: How to gate the computation of gradients. Can be

`GATE_NONE`, `GATE_OP`, or `GATE_GRAPH`.

aggregation_method: Specifies the method used to combine gradient terms.

Valid values are defined in the class `AggregationMethod`.

colocate_gradients_with_ops: If True, try colocating gradients with

the corresponding op.

grad_loss: Optional. A `Tensor` holding the gradient computed for `loss`.

Returns:

A list of (gradient, variable) pairs. Variable is always present, but

gradient can be `None`.

Raises:

TypeError: If `var_list` contains anything else than `Variable` objects.

ValueError: If some arguments are invalid.

RuntimeError: If called with eager execution enabled and `loss` is

not callable.

@compatibility(eager)

When eager execution is enabled, `gate_gradients`, `aggregation_method`,

and `colocate_gradients_with_ops` are ignored.

@end_compatibility

"""

if callable(loss):

with backprop.GradientTape() as tape:

if var_list is not None:

tape.watch(var_list)

loss_value = loss()

if var_list is None:

var_list = tape.watched_variables()

# TODO(jhseu): Figure out why GradientTape's gradients don't require loss

# to be executed.

with ops.control_dependencies([loss_value]):

grads = tape.gradient(loss_value, var_list, grad_loss)

return list(zip(grads, var_list))

# Non-callable/Tensor loss case

if context.executing_eagerly():

raise RuntimeError(

"`loss` passed to Optimizer.compute_gradients should "

"be a function when eager execution is enabled.")

if gate_gradients not in [Optimizer.GATE_NONE, Optimizer.GATE_OP,

Optimizer.GATE_GRAPH]:

raise ValueError("gate_gradients must be one of: Optimizer.GATE_NONE, "

"Optimizer.GATE_OP, Optimizer.GATE_GRAPH. Not %s" %

gate_gradients)

self._assert_valid_dtypes([loss])

if grad_loss is not None:

self._assert_valid_dtypes([grad_loss])

if var_list is None:

var_list = (

variables.trainable_variables() +

ops.get_collection(ops.GraphKeys.TRAINABLE_RESOURCE_VARIABLES))

else:

var_list = nest.flatten(var_list)

# pylint: disable=protected-access

var_list += ops.get_collection(ops.GraphKeys._STREAMING_MODEL_PORTS)

# pylint: enable=protected-access

processors = [_get_processor(v) for v in var_list]

if not var_list:

raise ValueError("No variables to optimize.")

var_refs = [p.target() for p in processors]

grads = gradients.gradients(

loss, var_refs, grad_ys=grad_loss,

gate_gradients=(gate_gradients == Optimizer.GATE_OP),

aggregation_method=aggregation_method,

colocate_gradients_with_ops=colocate_gradients_with_ops)

if gate_gradients == Optimizer.GATE_GRAPH:

grads = control_flow_ops.tuple(grads)

grads_and_vars = list(zip(grads, var_list))

self._assert_valid_dtypes(

[v for g, v in grads_and_vars

if g is not None and v.dtype != dtypes.resource])

return grads_and_vars

def apply_gradients(self, grads_and_vars, global_step=None, name=None):

"""Apply gradients to variables.

This is the second part of `minimize()`. It returns an `Operation` that

applies gradients.

Args:

grads_and_vars: List of (gradient, variable) pairs as returned by

`compute_gradients()`.

global_step: Optional `Variable` to increment by one after the

variables have been updated.

name: Optional name for the returned operation. Default to the

name passed to the `Optimizer` constructor.

Returns:

An `Operation` that applies the specified gradients. If `global_step`

was not None, that operation also increments `global_step`.

Raises:

TypeError: If `grads_and_vars` is malformed.

ValueError: If none of the variables have gradients.

RuntimeError: If you should use `_distributed_apply()` instead.

"""

# This is a default implementation of apply_gradients() that can be shared

# by most optimizers. It relies on the subclass implementing the following

# methods: _create_slots(), _prepare(), _apply_dense(), and _apply_sparse().

# TODO(isaprykin): Get rid of `has_strategy()` check by

# always calling _distributed_apply(), using the default distribution

# as needed.

if distribute_ctx.has_strategy():

# Handle DistributionStrategy case.

if distribute_ctx.in_cross_replica_context():

raise RuntimeError("Use `_distributed_apply()` instead of "

"`apply_gradients()` in a cross-replica context.")

grads_and_vars = get_filtered_grad_fn(lambda: grads_and_vars)()

return distribute_ctx.get_replica_context().merge_call(

self._distributed_apply, args=(grads_and_vars, global_step, name))

# No DistributionStrategy case.

grads_and_vars = tuple(grads_and_vars) # Make sure repeat iteration works.

if not grads_and_vars:

raise ValueError("No variables provided.")

converted_grads_and_vars = []

for g, v in grads_and_vars:

if g is not None:

try:

# Convert the grad to Tensor or IndexedSlices if necessary.

g = ops.convert_to_tensor_or_indexed_slices(g)

except TypeError:

raise TypeError(

"Gradient must be convertible to a Tensor"

" or IndexedSlices, or None: %s" % g)

if not isinstance(g, (ops.Tensor, ops.IndexedSlices)):

raise TypeError(

"Gradient must be a Tensor, IndexedSlices, or None: %s" % g)

p = _get_processor(v)

converted_grads_and_vars.append((g, v, p))

converted_grads_and_vars = tuple(converted_grads_and_vars)

var_list = [v for g, v, _ in converted_grads_and_vars if g is not None]

if not var_list:

raise ValueError("No gradients provided for any variable: %s." %

([str(v) for _, v, _ in converted_grads_and_vars],))

with ops.init_scope():

self._create_slots(var_list)

update_ops = []

with ops.name_scope(name, self._name) as name:

self._prepare()

for grad, var, processor in converted_grads_and_vars:

if grad is None:

continue

# We colocate all ops created in _apply_dense or _apply_sparse

# on the same device as the variable.

# TODO(apassos): figure out how to get the variable name here.

if context.executing_eagerly() or isinstance(

var,

resource_variable_ops.ResourceVariable) and not var._in_graph_mode: # pylint: disable=protected-access

scope_name = ""

else:

scope_name = var.op.name

with ops.name_scope("update_" + scope_name), ops.colocate_with(var):

update_ops.append(processor.update_op(self, grad))

if global_step is None:

apply_updates = self._finish(update_ops, name)

else:

with ops.control_dependencies([self._finish(update_ops, "update")]):

with ops.colocate_with(global_step):

if isinstance(global_step, resource_variable_ops.ResourceVariable):

# TODO(apassos): the implicit read in assign_add is slow; consider

# making it less so.

apply_updates = resource_variable_ops.assign_add_variable_op(

global_step.handle,

ops.convert_to_tensor(1, dtype=global_step.dtype),

name=name)

else:

apply_updates = state_ops.assign_add(global_step, 1, name=name)

if not context.executing_eagerly():

if isinstance(apply_updates, ops.Tensor):

apply_updates = apply_updates.op

train_op = ops.get_collection_ref(ops.GraphKeys.TRAIN_OP)

if apply_updates not in train_op:

train_op.append(apply_updates)

return apply_updates

def _distributed_apply(self,

distribution,

grads_and_vars,

global_step=None,

name=None):

"""A version of `apply_gradients` for cross-replica context.

This is a version of `apply_gradients()` for when you are using a

`DistributionStrategy` and are in a cross-replica context. If in a

replica context, use `apply_gradients()` as normal.

Args:

distribution: A `DistributionStrategy` object.

grads_and_vars: List of (gradient, variable) pairs as returned by

`compute_gradients()`, and then aggregated across replicas.

global_step: Optional (mirrored) `Variable` to increment by one

after the variables have been updated.

name: Optional name for the returned operation. Default to the

name passed to the `Optimizer` constructor.

Returns:

An `Operation` that applies the specified gradients across all

replicas. If `global_step` was not None, that operation also

increments `global_step`

"""

reduced_grads = distribution.extended.batch_reduce_to(

ds_reduce_util.ReduceOp.SUM, grads_and_vars)

var_list = [v for _, v in grads_and_vars]

grads_and_vars = zip(reduced_grads, var_list)

# Note that this is called in a cross-replica context.

with ops.init_scope():

self._create_slots(var_list)

def update(v, g):

"""Apply gradients to a replica variable."""

assert v is not None

try:

# Convert the grad to Tensor or IndexedSlices if necessary.

g = ops.convert_to_tensor_or_indexed_slices(g)

except TypeError:

raise TypeError("Gradient must be convertible to a Tensor"

" or IndexedSlices, or None: %s" % g)

if not isinstance(g, (ops.Tensor, ops.IndexedSlices)):

raise TypeError(

"Gradient must be a Tensor, IndexedSlices, or None: %s" % g)

p = _get_processor(v)

if context.executing_eagerly() or (

resource_variable_ops.is_resource_variable(v) and

not v._in_graph_mode): # pylint: disable=protected-access

scope_name = v.name.split(":")[0]

else:

scope_name = v.op.name

# device_policy is set because non-mirrored tensors will be read in

# `update_op`. `_resource_apply_dense`, `lr_t`, `beta1_t` and `beta2_t`

# is an example.

with ops.name_scope("update_" + scope_name):

return p.update_op(self, g)

with ops.name_scope(name, self._name) as name:

self._prepare()

update_ops = [

op

for grad, var in grads_and_vars

for op in distribution.extended.update(

var, update, args=(grad,), group=False)

]

def finish(self, update_ops):

return self._finish(update_ops, "update")

non_slot_devices = distribution.extended.non_slot_devices(var_list)

finish_updates = distribution.extended.update_non_slot(

non_slot_devices, finish, args=(self, update_ops), group=False)

if global_step is None:

apply_updates = distribution.group(finish_updates, name=name)

else:

with ops.control_dependencies(finish_updates):

apply_updates = distribution.extended.update(

global_step, state_ops.assign_add, args=(1,),

kwargs={"name": name})

if not context.executing_eagerly():

if isinstance(apply_updates, ops.Tensor):

apply_updates = apply_updates.op

train_op = ops.get_collection_ref(ops.GraphKeys.TRAIN_OP)

if apply_updates not in train_op:

train_op.append(apply_updates)

return apply_updates

def get_slot(self, var, name):

"""Return a slot named `name` created for `var` by the Optimizer.

Some `Optimizer` subclasses use additional variables. For example

`Momentum` and `Adagrad` use variables to accumulate updates. This method

gives access to these `Variable` objects if for some reason you need them.

Use `get_slot_names()` to get the list of slot names created by the

`Optimizer`.

Args:

var: A variable passed to `minimize()` or `apply_gradients()`.

name: A string.

Returns:

The `Variable` for the slot if it was created, `None` otherwise.

"""

# pylint: disable=protected-access

named_slots = self._slots.get(name, None)

if not named_slots:

return None

if hasattr(var, "_distributed_container"):

# NOTE: If this isn't patched, then there is no `handle` in

# `_resource_apply_dense`.

distributed_container = var._distributed_container()

assert distributed_container is not None

if ops.executing_eagerly_outside_functions():

key = distributed_container._unique_id

else:

key = (distributed_container.graph, distributed_container._shared_name)

# pylint: enable=protected-access

mirrored_slot = named_slots.get(key, None)

if mirrored_slot is None: return None

return mirrored_slot.get(device=var.device)

return named_slots.get(_var_key(var), None)

def get_slot_names(self):

"""Return a list of the names of slots created by the `Optimizer`.

See `get_slot()`.

Returns:

A list of strings.

"""

return sorted(self._slots.keys())

def variables(self):

"""A list of variables which encode the current state of `Optimizer`.

Includes slot variables and additional global variables created by the

optimizer in the current default graph.

Returns:

A list of variables.

"""

current_graph = ops.get_default_graph()

def _from_current_graph(variable):

if variable._in_graph_mode: # pylint: disable=protected-access

return variable.op.graph is current_graph

else:

# No variable.op in eager mode. We don't expect lots of eager graphs,

# but behavior should be consistent with graph mode.

return variable._graph_key == current_graph._graph_key # pylint: disable=protected-access

optimizer_variables = [v for v in self._non_slot_variables()

if _from_current_graph(v)]

for _, variable_dict in self._slots.items():

for _, slot_for_variable in variable_dict.items():

if _from_current_graph(slot_for_variable):

optimizer_variables.append(slot_for_variable)

# Sort variables by name so that the return is deterministic.

return sorted(optimizer_variables, key=lambda v: v.name)

def _create_non_slot_variable(self, initial_value, name, colocate_with):

"""Add an extra variable, not associated with a slot."""

# Recommendation: Use OptimizerV2 if your optimizer uses non-slot variables.

eager = context.executing_eagerly()

graph = None if eager else colocate_with.graph

key = (name, graph)

v = self._non_slot_dict.get(key, None)

if v is None:

self._maybe_initialize_trackable()

distribution_strategy = distribute_ctx.get_strategy()

with distribution_strategy.extended.colocate_vars_with(colocate_with):

if eager:

restored_initial_value = self._preload_simple_restoration(

name=name, shape=None)

if restored_initial_value is not None:

initial_value = restored_initial_value

v = variable_scope.variable(

initial_value, name=name, trainable=False,

use_resource=resource_variable_ops.is_resource_variable(

colocate_with))

# Restore this variable by name if necessary, but don't add a

# Trackable dependency. Optimizers return the current graph's

# non-slot variables from _checkpoint_dependencies explicitly rather

# than unconditionally adding dependencies (since there may be multiple

# non-slot variables with the same name in different graphs, trying to

# save all of them would result in errors).

self._handle_deferred_dependencies(name=name, trackable=v)

self._non_slot_dict[key] = v

return v

@property

def _checkpoint_dependencies(self):

"""From Trackable. Gather graph-specific non-slot variables to save."""

current_graph_non_slot_variables = []

current_graph_key = ops.get_default_graph()._graph_key # pylint: disable=protected-access

for (name, _), variable_object in sorted(self._non_slot_dict.items(),

# Avoid comparing graphs

key=lambda item: item[0][0]):

if variable_object._graph_key == current_graph_key: # pylint: disable=protected-access

current_graph_non_slot_variables.append(

trackable.TrackableReference(

name=name, ref=variable_object))

return (super(Optimizer, self)._checkpoint_dependencies

+ current_graph_non_slot_variables)

def _lookup_dependency(self, name):

"""From Trackable. Find a non-slot variable in the current graph."""

unconditional = super(Optimizer, self)._lookup_dependency(name)

if unconditional is not None:

return unconditional

graph = None if context.executing_eagerly() else ops.get_default_graph()

return self._get_non_slot_variable(name, graph=graph)

def _get_non_slot_variable(self, name, graph=None):

non_slot = self._non_slot_dict.get((name, graph), None)

if hasattr(non_slot, "_distributed_container"):

# This is a mirrored non-slot. In order to enable code like `_finish`

# to assign to a non-slot, return the current context replica.

return non_slot.get()

else:

return non_slot

def _non_slot_variables(self):

"""Additional variables created by the `Optimizer`.

Returns:

A list or tuple of variables.

"""

return self._non_slot_dict.values()

def _assert_valid_dtypes(self, tensors):

"""Asserts tensors are all valid types (see `_valid_dtypes`).

Args:

tensors: Tensors to check.

Raises:

ValueError: If any tensor is not a valid type.

"""

valid_dtypes = self._valid_dtypes()

for t in tensors:

dtype = t.dtype.base_dtype

if dtype not in valid_dtypes:

raise ValueError(

"Invalid type %r for %s, expected: %s." % (

dtype, t.name, [v for v in valid_dtypes]))

# --------------

# Methods to be implemented by subclasses if they want to use the

# inherited implementation of apply_gradients() or compute_gradients().

# --------------

def _valid_dtypes(self):

"""Valid types for loss, variables and gradients.

Subclasses should override to allow other float types.

Returns:

Valid types for loss, variables and gradients.

"""

return set(

[dtypes.float16, dtypes.bfloat16, dtypes.float32, dtypes.float64])

def _create_slots(self, var_list):

"""Create all slots needed by the variables.

Args:

var_list: A list of `Variable` objects.

"""

# No slots needed by default

pass

def _prepare(self):

"""Create all needed tensors before applying gradients.

This is called with the name_scope using the "name" that

users have chosen for the application of gradients.

"""

pass

def _apply_dense(self, grad, var):

"""Add ops to apply dense gradients to `var`.

Args:

grad: A `Tensor`.

var: A `Variable` object.

Returns:

An `Operation`.

"""

raise NotImplementedError()

def _resource_apply_dense(self, grad, handle):

"""Add ops to apply dense gradients to the variable `handle`.

Args:

grad: a `Tensor` representing the gradient.

handle: a `Tensor` of dtype `resource` which points to the variable

to be updated.

Returns:

An `Operation` which updates the value of the variable.

"""

raise NotImplementedError()

def _resource_apply_sparse_duplicate_indices(self, grad, handle, indices):

"""Add ops to apply sparse gradients to `handle`, with repeated indices.

Optimizers which override this method must deal with repeated indices. See

the docstring of `_apply_sparse_duplicate_indices` for details. By default

the correct behavior, to sum non-unique indices and their associated

gradients, is enforced by first pre-processing `grad` and `indices` and

passing them on to `_resource_apply_sparse`. Optimizers which deal correctly

with duplicate indices may instead override this method to avoid the

overhead of summing.

Args:

grad: a `Tensor` representing the gradient for the affected indices.

handle: a `Tensor` of dtype `resource` which points to the variable

to be updated.

indices: a `Tensor` of integral type representing the indices for

which the gradient is nonzero. Indices may be repeated.

Returns:

An `Operation` which updates the value of the variable.

"""

summed_grad, unique_indices = _deduplicate_indexed_slices(

values=grad, indices=indices)

return self._resource_apply_sparse(summed_grad, handle, unique_indices)

def _resource_apply_sparse(self, grad, handle, indices):

"""Add ops to apply sparse gradients to the variable `handle`.

Similar to `_apply_sparse`, the `indices` argument to this method has been

de-duplicated. Optimizers which deal correctly with non-unique indices may

instead override `_resource_apply_sparse_duplicate_indices` to avoid this

overhead.

Args:

grad: a `Tensor` representing the gradient for the affected indices.

handle: a `Tensor` of dtype `resource` which points to the variable

to be updated.

indices: a `Tensor` of integral type representing the indices for

which the gradient is nonzero. Indices are unique.

Returns:

An `Operation` which updates the value of the variable.

"""

raise NotImplementedError()

def _apply_sparse_duplicate_indices(self, grad, var):

"""Add ops to apply sparse gradients to `var`, with repeated sparse indices.

Optimizers which override this method must deal with IndexedSlices objects

such as the following:

IndexedSlicesValue(values=[1, 1], indices=[0, 0], dense_shape=[1])

The correct interpretation is:

IndexedSlicesValue(values=[2], indices=[0], dense_shape=[1])

Many optimizers deal incorrectly with repeated indices when updating based

on sparse gradients (e.g. summing squares rather than squaring the sum, or

applying momentum terms multiple times). Adding first is always the correct

behavior, so this is enforced here by reconstructing the IndexedSlices to

have only unique indices, then calling _apply_sparse.

Optimizers which deal correctly with repeated indices may instead override

this method to avoid the overhead of summing indices.