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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.
# ==============================================================================
"""Layers that act as activation functions.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
from tensorflow.python.keras._impl.keras import activations
from tensorflow.python.keras._impl.keras import backend as K
from tensorflow.python.keras._impl.keras import constraints
from tensorflow.python.keras._impl.keras import initializers
from tensorflow.python.keras._impl.keras import regularizers
from tensorflow.python.keras._impl.keras.engine import InputSpec
from tensorflow.python.keras._impl.keras.engine import Layer
from tensorflow.python.keras._impl.keras.engine.base_layer import shape_type_conversion
from tensorflow.python.ops import math_ops
from tensorflow.python.util.tf_export import tf_export
@tf_export('keras.layers.LeakyReLU')
class LeakyReLU(Layer):
"""Leaky version of a Rectified Linear Unit.
It allows a small gradient when the unit is not active:
`f(x) = alpha * x for x < 0`,
`f(x) = x for x >= 0`.
Input shape:
Arbitrary. Use the keyword argument `input_shape`
(tuple of integers, does not include the samples axis)
when using this layer as the first layer in a model.
Output shape:
Same shape as the input.
Arguments:
alpha: float >= 0. Negative slope coefficient.
"""
def __init__(self, alpha=0.3, **kwargs):
super(LeakyReLU, self).__init__(**kwargs)
self.supports_masking = True
self.alpha = K.cast_to_floatx(alpha)
def call(self, inputs):
return K.relu(inputs, alpha=self.alpha)
def get_config(self):
config = {'alpha': float(self.alpha)}
base_config = super(LeakyReLU, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
@shape_type_conversion
def compute_output_shape(self, input_shape):
return input_shape
@tf_export('keras.layers.PReLU')
class PReLU(Layer):
"""Parametric Rectified Linear Unit.
It follows:
`f(x) = alpha * x for x < 0`,
`f(x) = x for x >= 0`,
where `alpha` is a learned array with the same shape as x.
Input shape:
Arbitrary. Use the keyword argument `input_shape`
(tuple of integers, does not include the samples axis)
when using this layer as the first layer in a model.
Output shape:
Same shape as the input.
Arguments:
alpha_initializer: initializer function for the weights.
alpha_regularizer: regularizer for the weights.
alpha_constraint: constraint for the weights.
shared_axes: the axes along which to share learnable
parameters for the activation function.
For example, if the incoming feature maps
are from a 2D convolution
with output shape `(batch, height, width, channels)`,
and you wish to share parameters across space
so that each filter only has one set of parameters,
set `shared_axes=[1, 2]`.
"""
def __init__(self,
alpha_initializer='zeros',
alpha_regularizer=None,
alpha_constraint=None,
shared_axes=None,
**kwargs):
super(PReLU, self).__init__(**kwargs)
self.supports_masking = True
self.alpha_initializer = initializers.get(alpha_initializer)
self.alpha_regularizer = regularizers.get(alpha_regularizer)
self.alpha_constraint = constraints.get(alpha_constraint)
if shared_axes is None:
self.shared_axes = None
elif not isinstance(shared_axes, (list, tuple)):
self.shared_axes = [shared_axes]
else:
self.shared_axes = list(shared_axes)
@shape_type_conversion
def build(self, input_shape):
param_shape = list(input_shape[1:])
self.param_broadcast = [False] * len(param_shape)
if self.shared_axes is not None:
for i in self.shared_axes:
param_shape[i - 1] = 1
self.param_broadcast[i - 1] = True
self.alpha = self.add_weight(
shape=param_shape,
name='alpha',
initializer=self.alpha_initializer,
regularizer=self.alpha_regularizer,
constraint=self.alpha_constraint)
# Set input spec
axes = {}
if self.shared_axes:
for i in range(1, len(input_shape)):
if i not in self.shared_axes:
axes[i] = input_shape[i]
self.input_spec = InputSpec(ndim=len(input_shape), axes=axes)
self.built = True
def call(self, inputs, mask=None):
pos = K.relu(inputs)
if K.backend() == 'theano':
neg = (
K.pattern_broadcast(self.alpha, self.param_broadcast) *
(inputs - math_ops.abs(inputs)) * 0.5)
else:
neg = -self.alpha * K.relu(-inputs)
return pos + neg
def get_config(self):
config = {
'alpha_initializer': initializers.serialize(self.alpha_initializer),
'alpha_regularizer': regularizers.serialize(self.alpha_regularizer),
'alpha_constraint': constraints.serialize(self.alpha_constraint),
'shared_axes': self.shared_axes
}
base_config = super(PReLU, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
@shape_type_conversion
def compute_output_shape(self, input_shape):
return input_shape
@tf_export('keras.layers.ELU')
class ELU(Layer):
"""Exponential Linear Unit.
It follows:
`f(x) = alpha * (exp(x) - 1.) for x < 0`,
`f(x) = x for x >= 0`.
Input shape:
Arbitrary. Use the keyword argument `input_shape`
(tuple of integers, does not include the samples axis)
when using this layer as the first layer in a model.
Output shape:
Same shape as the input.
Arguments:
alpha: scale for the negative factor.
"""
def __init__(self, alpha=1.0, **kwargs):
super(ELU, self).__init__(**kwargs)
self.supports_masking = True
self.alpha = K.cast_to_floatx(alpha)
def call(self, inputs):
return K.elu(inputs, self.alpha)
def get_config(self):
config = {'alpha': float(self.alpha)}
base_config = super(ELU, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
@shape_type_conversion
def compute_output_shape(self, input_shape):
return input_shape
@tf_export('keras.layers.ThresholdedReLU')
class ThresholdedReLU(Layer):
"""Thresholded Rectified Linear Unit.
It follows:
`f(x) = x for x > theta`,
`f(x) = 0 otherwise`.
Input shape:
Arbitrary. Use the keyword argument `input_shape`
(tuple of integers, does not include the samples axis)
when using this layer as the first layer in a model.
Output shape:
Same shape as the input.
Arguments:
theta: float >= 0. Threshold location of activation.
"""
def __init__(self, theta=1.0, **kwargs):
super(ThresholdedReLU, self).__init__(**kwargs)
self.supports_masking = True
self.theta = K.cast_to_floatx(theta)
def call(self, inputs, mask=None):
return inputs * math_ops.cast(
math_ops.greater(inputs, self.theta), K.floatx())
def get_config(self):
config = {'theta': float(self.theta)}
base_config = super(ThresholdedReLU, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
@shape_type_conversion
def compute_output_shape(self, input_shape):
return input_shape
@tf_export('keras.layers.Softmax')
class Softmax(Layer):
"""Softmax activation function.
Input shape:
Arbitrary. Use the keyword argument `input_shape`
(tuple of integers, does not include the samples axis)
when using this layer as the first layer in a model.
Output shape:
Same shape as the input.
Arguments:
axis: Integer, axis along which the softmax normalization is applied.
"""
def __init__(self, axis=-1, **kwargs):
super(Softmax, self).__init__(**kwargs)
self.supports_masking = True
self.axis = axis
def call(self, inputs):
return activations.softmax(inputs, axis=self.axis)
def get_config(self):
config = {'axis': self.axis}
base_config = super(Softmax, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
@shape_type_conversion
def compute_output_shape(self, input_shape):
return input_shape