def linear_classifier(embeddings, num_classes, cosine_classifier,
cosine_logits_multiplier, use_weight_norm, weight_decay):
"""Forward pass through a linear classifier, or possibly a cosine classifier.
Args:
embeddings: A Tensor of size [batch size, embedding dim].
num_classes: An integer; the dimension of the classification.
cosine_classifier: A bool. If true, a cosine classifier is used, which does
not require a bias.
cosine_logits_multiplier: A float. Only used if cosine_classifier is True,
and multiplies the resulting logits.
use_weight_norm: A bool. Whether weight norm was used. If so, then if using
cosine classifier, normalize only the embeddings but not the weights.
weight_decay: A float; the scalar multiple on the L2 regularization of the
weight matrix.
Returns:
logits: A Tensor of size [batch size, num outputs].
"""
embedding_dims = embeddings.get_shape().as_list()[-1]
if use_weight_norm:
# A variable to keep track of whether the initialization has already
# happened.
data_dependent_init_done = tf.get_variable('data_dependent_init_done',
initializer=0,
dtype=tf.int32,
trainable=False)
w_fc = tf.get_variable('w_fc', [embedding_dims, num_classes],
initializer=tf.random_normal_initializer(
0, 0.05),
trainable=True)
# This init is temporary as it needs to be done in a data-dependent way.
# It will be overwritten during the first forward pass through this layer.
g = tf.get_variable('g',
dtype=tf.float32,
initializer=tf.ones([num_classes]),
trainable=True)
b_fc = None
if not cosine_classifier:
# Also initialize a bias.
b_fc = tf.get_variable('b_fc',
initializer=tf.zeros([num_classes]),
trainable=True)
def _do_data_dependent_init():
"""Returns ops for the data-dependent init of g and maybe b_fc."""
w_fc_normalized = tf.nn.l2_normalize(w_fc.read_value(), [0])
output_init = tf.matmul(embeddings, w_fc_normalized)
mean_init, var_init = tf.nn.moments(output_init, [0])
# Data-dependent init values.
g_init_value = 1. / tf.sqrt(var_init + 1e-10)
ops = [tf.assign(g, g_init_value)]
if not cosine_classifier:
# Also initialize a bias in a data-dependent way.
b_fc_init_value = -mean_init * g_init_value
ops.append(tf.assign(b_fc, b_fc_init_value))
# Mark that the data-dependent initialization is done to prevent it from
# happening again in the future.
ops.append(tf.assign(data_dependent_init_done, 1))
return tf.group(*ops)
# Possibly perform data-dependent init (if it hasn't been done already).
init_op = tf.cond(tf.equal(data_dependent_init_done, 0),
_do_data_dependent_init, tf.no_op)
with tf.control_dependencies([init_op]):
# Apply weight normalization.
w_fc *= g / tf.sqrt(tf.reduce_sum(tf.square(w_fc), [0]))
# Forward pass through the layer defined by w_fc and b_fc.
logits = linear_classifier_forward_pass(embeddings, w_fc, b_fc,
cosine_classifier,
cosine_logits_multiplier,
True)
else:
# No weight norm.
w_fc = functional_backbones.weight_variable(
[embedding_dims, num_classes], weight_decay=weight_decay)
b_fc = None
if not cosine_classifier:
# Also initialize a bias.
b_fc = functional_backbones.bias_variable([num_classes])
# Forward pass through the layer defined by w_fc and b_fc.
logits = linear_classifier_forward_pass(embeddings, w_fc, b_fc,
cosine_classifier,
cosine_logits_multiplier,
False)
return logits
def forward_pass(self, data):
"""Computes the test logits of MAML.
Args:
data: A `meta_dataset.providers.Episode` containing the data for the
episode.
Returns:
The output logits for the query data in this episode.
"""
# Have to use one-hot labels since sparse softmax doesn't allow
# second derivatives.
support_embeddings_ = self.embedding_fn(
data.support_images, self.is_training, reuse=tf.AUTO_REUSE)
support_embeddings = support_embeddings_['embeddings']
embedding_vars_dict = support_embeddings_['params']
# TODO(eringrant): Refactor to make use of
# `functional_backbones.linear_classifier`, which allows Gin-configuration.
with tf.variable_scope('linear_classifier', reuse=tf.AUTO_REUSE):
embedding_depth = support_embeddings.shape.as_list()[-1]
fc_weights = functional_backbones.weight_variable(
[embedding_depth, self.logit_dim],
weight_decay=self.classifier_weight_decay)
fc_bias = functional_backbones.bias_variable([self.logit_dim])
# A list of variable names, a list of corresponding Variables, and a list
# of operations (possibly empty) that creates a copy of each Variable.
(embedding_vars_keys, embedding_vars,
embedding_vars_copy_ops) = get_embeddings_vars_copy_ops(
embedding_vars_dict, make_copies=not self.is_training)
# A Variable for the weights of the fc layer, a Variable for the bias of the
# fc layer, and a list of operations (possibly empty) that copies them.
(fc_weights, fc_bias, fc_vars_copy_ops) = get_fc_vars_copy_ops(
fc_weights, fc_bias, make_copies=not self.is_training)
fc_vars = [fc_weights, fc_bias]
num_embedding_vars = len(embedding_vars)
num_fc_vars = len(fc_vars)
def _cond(step, *args):
del args
num_steps = self.num_update_steps
if not self.is_training:
num_steps += self.additional_evaluation_update_steps
return step < num_steps
def _body(step, *args):
"""The inner update loop body."""
updated_embedding_vars = args[0:num_embedding_vars]
updated_fc_vars = args[num_embedding_vars:num_embedding_vars +
num_fc_vars]
support_embeddings = self.embedding_fn(
data.support_images,
self.is_training,
params=collections.OrderedDict(
zip(embedding_vars_keys, updated_embedding_vars)),
reuse=True)['embeddings']
updated_fc_weights, updated_fc_bias = updated_fc_vars
support_logits = tf.matmul(support_embeddings,
updated_fc_weights) + updated_fc_bias
support_logits = support_logits[:, 0:data.way]
loss = tf.losses.softmax_cross_entropy(data.onehot_support_labels,
support_logits)
print_op = tf.no_op()
if self.debug_log:
print_op = tf.print(['step: ', step, updated_fc_bias[0], 'loss:', loss])
with tf.control_dependencies([print_op]):
updated_embedding_vars = gradient_descent_step(
loss, updated_embedding_vars, self.first_order,
self.adapt_batch_norm, self.alpha, False)['updated_vars']
updated_fc_vars = gradient_descent_step(loss, updated_fc_vars,
self.first_order,
self.adapt_batch_norm,
self.alpha,
False)['updated_vars']
step = step + 1
return tuple([step] + list(updated_embedding_vars) +
list(updated_fc_vars))
# MAML meta updates using query set examples from an episode.
if self.zero_fc_layer:
# To account for variable class sizes, we initialize the output
# weights to zero. See if truncated normal initialization will help.
zero_weights_op = tf.assign(fc_weights, tf.zeros_like(fc_weights))
zero_bias_op = tf.assign(fc_bias, tf.zeros_like(fc_bias))
fc_vars_init_ops = [zero_weights_op, zero_bias_op]
else:
fc_vars_init_ops = fc_vars_copy_ops
if self.proto_maml_fc_layer_init:
support_embeddings = self.embedding_fn(
data.support_images,
self.is_training,
params=collections.OrderedDict(
zip(embedding_vars_keys, embedding_vars)),
reuse=True)['embeddings']
prototypes = metric_learners.compute_prototypes(
support_embeddings, data.onehot_support_labels)
pmaml_fc_weights = self.proto_maml_fc_weights(
prototypes, zero_pad_to_max_way=True)
pmaml_fc_bias = self.proto_maml_fc_bias(
prototypes, zero_pad_to_max_way=True)
fc_vars = [pmaml_fc_weights, pmaml_fc_bias]
# These control dependencies assign the value of each variable to a new copy
# variable that corresponds to it. This is required at test time for
# initilizing the copies as they are used in place of the original vars.
with tf.control_dependencies(fc_vars_init_ops + embedding_vars_copy_ops):
# Make step a local variable as we don't want to save and restore it.
step = tf.Variable(
0,
trainable=False,
name='inner_step_counter',
collections=[tf.GraphKeys.LOCAL_VARIABLES])
loop_vars = [step] + embedding_vars + fc_vars
step_and_all_updated_vars = tf.while_loop(
_cond, _body, loop_vars, swap_memory=True)
step = step_and_all_updated_vars[0]
all_updated_vars = step_and_all_updated_vars[1:]
updated_embedding_vars = all_updated_vars[0:num_embedding_vars]
updated_fc_weights, updated_fc_bias = all_updated_vars[
num_embedding_vars:num_embedding_vars + num_fc_vars]
# Forward pass the training images with the updated weights in order to
# compute the means and variances, to use for the query's batch norm.
support_set_moments = None
if not self.transductive_batch_norm:
support_set_moments = self.embedding_fn(
data.support_images,
self.is_training,
params=collections.OrderedDict(
zip(embedding_vars_keys, updated_embedding_vars)),
reuse=True)['moments']
query_embeddings = self.embedding_fn(
data.query_images,
self.is_training,
params=collections.OrderedDict(
zip(embedding_vars_keys, updated_embedding_vars)),
moments=support_set_moments, # Use support set stats for batch norm.
reuse=True,
backprop_through_moments=self.backprop_through_moments)['embeddings']
query_logits = (tf.matmul(query_embeddings, updated_fc_weights) +
updated_fc_bias)[:, 0:data.way]
return query_logits