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video_level_models.py
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video_level_models.py
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# Copyright 2016 Google Inc. 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.
"""Contains model definitions."""
import math
import models
import tensorflow as tf
import utils
from tensorflow import flags
import tensorflow.contrib.slim as slim
FLAGS = flags.FLAGS
flags.DEFINE_integer(
"moe_num_mixtures", 2,
"The number of mixtures (excluding the dummy 'expert') used for MoeModel.")
class LogisticModel(models.BaseModel):
"""Logistic model with L2 regularization."""
def create_model(self,
model_input,
vocab_size,
l2_penalty=1e-8,
**unused_params):
"""Creates a logistic model.
Args:
model_input: 'batch' x 'num_features' matrix of input features.
vocab_size: The number of classes in the dataset.
Returns:
A dictionary with a tensor containing the probability predictions of the
model in the 'predictions' key. The dimensions of the tensor are
batch_size x num_classes.
"""
output = slim.fully_connected(
model_input,
vocab_size,
activation_fn=tf.nn.sigmoid,
weights_regularizer=slim.l2_regularizer(l2_penalty))
return {"predictions": output}
class MoeModel(models.BaseModel):
"""A softmax over a mixture of logistic models (with L2 regularization)."""
def create_model(self,
model_input,
vocab_size,
num_mixtures=None,
l2_penalty=1e-8,
**unused_params):
"""Creates a Mixture of (Logistic) Experts model.
The model consists of a per-class softmax distribution over a
configurable number of logistic classifiers. One of the classifiers in the
mixture is not trained, and always predicts 0.
Args:
model_input: 'batch_size' x 'num_features' matrix of input features.
vocab_size: The number of classes in the dataset.
num_mixtures: The number of mixtures (excluding a dummy 'expert' that
always predicts the non-existence of an entity).
l2_penalty: How much to penalize the squared magnitudes of parameter
values.
Returns:
A dictionary with a tensor containing the probability predictions of the
model in the 'predictions' key. The dimensions of the tensor are
batch_size x num_classes.
"""
num_mixtures = num_mixtures or FLAGS.moe_num_mixtures
gate_activations = slim.fully_connected(
model_input,
vocab_size * (num_mixtures + 1),
activation_fn=None,
biases_initializer=None,
weights_regularizer=slim.l2_regularizer(l2_penalty),
scope="gates")
expert_activations = slim.fully_connected(
model_input,
vocab_size * num_mixtures,
activation_fn=None,
weights_regularizer=slim.l2_regularizer(l2_penalty),
scope="experts")
gating_distribution = tf.nn.softmax(
tf.reshape(
gate_activations,
[-1, num_mixtures + 1])) # (Batch * #Labels) x (num_mixtures + 1)
expert_distribution = tf.nn.sigmoid(
tf.reshape(expert_activations,
[-1, num_mixtures])) # (Batch * #Labels) x num_mixtures
final_probabilities_by_class_and_batch = tf.reduce_sum(
gating_distribution[:, :num_mixtures] * expert_distribution, 1)
final_probabilities = tf.reshape(final_probabilities_by_class_and_batch,
[-1, vocab_size])
return {"predictions": final_probabilities}