161 lines
6.7 KiB
Python
161 lines
6.7 KiB
Python
# Copyright 2018 The TensorFlow Authors. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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# ==============================================================================
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"""Adadelta optimizer implementation."""
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# pylint: disable=g-classes-have-attributes
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from __future__ import absolute_import
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from __future__ import division
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from __future__ import print_function
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import numpy as np
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from tensorflow.python.framework import ops
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from tensorflow.python.keras import backend_config
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from tensorflow.python.keras.optimizer_v2 import optimizer_v2
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from tensorflow.python.ops import array_ops
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from tensorflow.python.training import gen_training_ops
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from tensorflow.python.util.tf_export import keras_export
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@keras_export('keras.optimizers.Adadelta')
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class Adadelta(optimizer_v2.OptimizerV2):
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r"""Optimizer that implements the Adadelta algorithm.
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Adadelta optimization is a stochastic gradient descent method that is based on
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adaptive learning rate per dimension to address two drawbacks:
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- The continual decay of learning rates throughout training
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- The need for a manually selected global learning rate
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Adadelta is a more robust extension of Adagrad that adapts learning rates
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based on a moving window of gradient updates, instead of accumulating all
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past gradients. This way, Adadelta continues learning even when many updates
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have been done. Compared to Adagrad, in the original version of Adadelta you
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don't have to set an initial learning rate. In this version, initial
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learning rate can be set, as in most other Keras optimizers.
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According to section 4.3 ("Effective Learning rates"), near the end of
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training step sizes converge to 1 which is effectively a high learning
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rate which would cause divergence. This occurs only near the end of the
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training as gradients and step sizes are small, and the epsilon constant
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in the numerator and denominator dominate past gradients and parameter
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updates which converge the learning rate to 1.
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According to section 4.4("Speech Data"),where a large neural network with
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4 hidden layers was trained on a corpus of US English data, ADADELTA was
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used with 100 network replicas.The epsilon used is 1e-6 with rho=0.95
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which converged faster than ADAGRAD, by the following construction:
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def __init__(self, lr=1.0, rho=0.95, epsilon=1e-6, decay=0., **kwargs):
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Args:
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learning_rate: A `Tensor`, floating point value, or a schedule that is a
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`tf.keras.optimizers.schedules.LearningRateSchedule`. The learning rate.
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To match the exact form in the original paper use 1.0.
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rho: A `Tensor` or a floating point value. The decay rate.
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epsilon: A `Tensor` or a floating point value. A constant epsilon used
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to better conditioning the grad update.
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name: Optional name prefix for the operations created when applying
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gradients. Defaults to `"Adadelta"`.
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**kwargs: Keyword arguments. Allowed to be one of
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`"clipnorm"` or `"clipvalue"`.
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`"clipnorm"` (float) clips gradients by norm; `"clipvalue"` (float) clips
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gradients by value.
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Reference:
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- [Zeiler, 2012](http://arxiv.org/abs/1212.5701)
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"""
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_HAS_AGGREGATE_GRAD = True
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def __init__(self,
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learning_rate=0.001,
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rho=0.95,
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epsilon=1e-7,
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name='Adadelta',
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**kwargs):
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super(Adadelta, self).__init__(name, **kwargs)
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self._set_hyper('learning_rate', kwargs.get('lr', learning_rate))
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self._set_hyper('decay', self._initial_decay)
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self._set_hyper('rho', rho)
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self.epsilon = epsilon or backend_config.epsilon()
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def _create_slots(self, var_list):
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# Separate for-loops to respect the ordering of slot variables from v1.
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for v in var_list:
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self.add_slot(v, 'accum_grad')
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for v in var_list:
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self.add_slot(v, 'accum_var')
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def _prepare_local(self, var_device, var_dtype, apply_state):
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super(Adadelta, self)._prepare_local(var_device, var_dtype, apply_state)
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apply_state[(var_device, var_dtype)].update(
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dict(
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epsilon=ops.convert_to_tensor_v2_with_dispatch(
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self.epsilon, var_dtype),
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rho=array_ops.identity(self._get_hyper('rho', var_dtype))))
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def set_weights(self, weights):
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params = self.weights
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# Override set_weights for backward compatibility of Keras V1 optimizer
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# since it does not include iteration at head of the weight list. Set
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# iteration to 0.
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if len(params) == len(weights) + 1:
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weights = [np.array(0)] + weights
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super(Adadelta, self).set_weights(weights)
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def _resource_apply_dense(self, grad, var, apply_state=None):
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var_device, var_dtype = var.device, var.dtype.base_dtype
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coefficients = ((apply_state or {}).get((var_device, var_dtype))
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or self._fallback_apply_state(var_device, var_dtype))
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accum_grad = self.get_slot(var, 'accum_grad')
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accum_var = self.get_slot(var, 'accum_var')
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return gen_training_ops.ResourceApplyAdadelta(
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var=var.handle,
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accum=accum_grad.handle,
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accum_update=accum_var.handle,
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lr=coefficients['lr_t'],
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rho=coefficients['rho'],
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epsilon=coefficients['epsilon'],
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grad=grad,
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use_locking=self._use_locking)
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def _resource_apply_sparse(self, grad, var, indices, apply_state=None):
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var_device, var_dtype = var.device, var.dtype.base_dtype
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coefficients = ((apply_state or {}).get((var_device, var_dtype))
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or self._fallback_apply_state(var_device, var_dtype))
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accum_grad = self.get_slot(var, 'accum_grad')
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accum_var = self.get_slot(var, 'accum_var')
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return gen_training_ops.ResourceSparseApplyAdadelta(
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var=var.handle,
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accum=accum_grad.handle,
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accum_update=accum_var.handle,
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lr=coefficients['lr_t'],
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rho=coefficients['rho'],
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epsilon=coefficients['epsilon'],
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grad=grad,
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indices=indices,
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use_locking=self._use_locking)
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def get_config(self):
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config = super(Adadelta, self).get_config()
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config.update({
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'learning_rate': self._serialize_hyperparameter('learning_rate'),
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'decay': self._initial_decay,
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'rho': self._serialize_hyperparameter('rho'),
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'epsilon': self.epsilon,
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})
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return config
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