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# Numenta Platform for Intelligent Computing (NuPIC)
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# See the GNU Affero Public License for more details.
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import abc
import numpy as np
import tensorflow as tf
from tensorflow import keras
from tensorflow.python.keras import backend as K
IMAGE_DATA_FORMAT = K.image_data_format()
[docs]def compute_kwinners(x, k, duty_cycles, boost_strength):
r"""
Use the boost strength to compute a boost factor for each unit represented
in x. These factors are used to increase the impact of each unit to improve
their chances of being chosen. This encourages participation of more columns
in the learning process.
The boosting function is a curve defined as: boost_factors = exp[ -
boost_strength * (dutyCycle - target_density)] Intuitively this means that
units that have been active (i.e. in the top-k) at the target activation
level have a boost factor of 1, meaning their activity is not boosted.
Columns whose duty cycle drops too much below that of their neighbors are
boosted depending on how infrequently they have been active. Unit that has
been active more than the target activation level have a boost factor below
1, meaning their activity is suppressed and they are less likely to be in
the top-k.
Note that we do not transmit the boosted values. We only use boosting to
determine the winning units.
The target activation density for each unit is k / number of units. The
boostFactor depends on the dutyCycle via an exponential function::
boostFactor
^
|
|\
| \
1 _ | \
| _
| _ _
| _ _ _ _
+--------------------> dutyCycle
|
target_density
:param x:
Current activity of each unit.
:param k:
The activity of the top k units will be allowed to remain, the rest are
set to zero.
:param duty_cycles:
The averaged duty cycle of each unit.
:param boost_strength:
A boost strength of 0.0 has no effect on x.
:return:
A tensor representing the activity of x after k-winner take all.
"""
k = tf.convert_to_tensor(k, dtype=tf.int32)
x = tf.convert_to_tensor(x, dtype=tf.float32)
boost_strength = tf.math.maximum(boost_strength, 0.0)
input_shape = tf.shape(x)
batch_size = input_shape[0]
n = tf.reduce_prod(x.shape[1:])
target_density = tf.cast(k, tf.float32) / tf.cast(n, tf.float32)
boost_factors = tf.exp((target_density - duty_cycles) * boost_strength)
boosted = x * boost_factors
# Take the boosted version of the input x, find the top k winners.
# Compute an output that contains the values of x corresponding to the top k
# boosted values
boosted = tf.reshape(boosted, [batch_size, -1])
flat_x = tf.reshape(x, [batch_size, -1])
_, indices = tf.math.top_k(input=boosted, k=k, sorted=False)
mask = tf.reduce_sum(tf.one_hot(indices, tf.shape(boosted)[-1]), axis=1)
return tf.reshape(mask * flat_x, input_shape)
[docs]class KWinnersBase(keras.layers.Layer, metaclass=abc.ABCMeta):
"""
Base KWinners class.
:param percent_on:
The activity of the top k = percent_on * number of input units will be
allowed to remain, the rest are set to zero.
:type percent_on: float
:param k_inference_factor:
During inference (training=False) we increase percent_on by this factor.
percent_on * k_inference_factor must be strictly less than 1.0, ideally
much lower than 1.0
:type k_inference_factor: float
:param boost_strength:
boost strength (0.0 implies no boosting). Must be >= 0.0
:type boost_strength: float
:param boost_strength_factor:
Boost strength factor to use [0..1]
:type boost_strength_factor: float
:param duty_cycle_period:
The period used to calculate duty cycles
:type duty_cycle_period: int
:param kwargs:
Additional args passed to :class:`keras.layers.Layer`
:type kwargs: dict
"""
def __init__(
self,
percent_on,
k_inference_factor,
boost_strength,
boost_strength_factor,
duty_cycle_period,
name=None,
**kwargs,
):
super(KWinnersBase, self).__init__(name=name, **kwargs)
self.percent_on = percent_on
self.percent_on_inference = percent_on * k_inference_factor
self.k_inference_factor = k_inference_factor
self.learning_iterations = None
self.n = 0
self.k = 0
self.k_inference = 0
# Boosting related parameters
self.boost_strength = None
self.initial_boost_strength = boost_strength
self.boost_strength_factor = boost_strength_factor
self.duty_cycle_period = duty_cycle_period
self.duty_cycles = None
[docs] def build(self, input_shape):
super(KWinnersBase, self).build(input_shape=input_shape)
self.learning_iterations = self.add_variable(
name="learning_iterations",
shape=[],
initializer="zeros",
trainable=False,
dtype=tf.int32,
)
self.boost_strength = self.add_variable(
name="boost_strength",
shape=[],
initializer=keras.initializers.Constant(self.initial_boost_strength),
trainable=False,
dtype=tf.float32,
)
[docs] def get_config(self):
config = {
"percent_on": self.percent_on,
"k_inference_factor": self.k_inference_factor,
"boost_strength": K.get_value(self.boost_strength),
"boost_strength_factor": self.boost_strength_factor,
"duty_cycle_period": self.duty_cycle_period,
}
config.update(super(KWinnersBase, self).get_config())
return config
[docs] def compute_output_shape(self, input_shape):
return input_shape
[docs] @abc.abstractmethod
def compute_duty_cycle(self, x):
r"""
Compute our duty cycle estimates with the new value. Duty cycles are
updated according to the following formula:
.. math::
dutyCycle = \frac{dutyCycle \times \left( period - batchSize \right)
+ newValue}{period}
:param x:
Current activity of each unit
"""
raise NotImplementedError
[docs] def update_boost_strength(self):
"""
Update boost strength using given strength factor during training.
"""
factor = K.in_train_phase(self.boost_strength_factor, 1.0)
self.add_update(
self.boost_strength.assign(self.boost_strength * factor, read_value=False)
)
[docs] def call(self, inputs, **kwargs):
inputs = super().call(inputs, **kwargs)
# FIXME: In eager mode, predict_on_batch method is called with list of inputs
if isinstance(inputs, list) and len(inputs) == 1:
inputs = inputs[0]
return inputs
[docs]class KWinners2d(KWinnersBase):
"""
Applies K-Winner function to Conv2D input tensor.
:param percent_on:
The activity of the top k = percent_on * number of input units will be
allowed to remain, the rest are set to zero.
:type percent_on: float
:param k_inference_factor:
During inference (training=False) we increase percent_on by this factor.
percent_on * k_inference_factor must be strictly less than 1.0, ideally much
lower than 1.0
:type k_inference_factor: float
:param boost_strength:
boost strength (0.0 implies no boosting).
:type boost_strength: float
:param boost_strength_factor:
Boost strength factor to use [0..1]
:type boost_strength_factor: float
:param duty_cycle_period:
The period used to calculate duty cycles
:type duty_cycle_period: int
:param data_format:
one of `channels_first` or `channels_last`. The ordering of
the dimensions in the inputs. `channels_last` corresponds to inputs with
shape `(batch, height, width, channels)` while `channels_first` corresponds
to inputs with shape `(batch, channels, height, width)`.
Similar to `data_format` argument in :class:`keras.layers.Conv2D`.
:type data_format: str
:param kwargs:
Additional args passed to :class:`keras.layers.Layer`
:type kwargs: dict
"""
def __init__(
self,
percent_on=0.1,
k_inference_factor=1.5,
boost_strength=1.0,
boost_strength_factor=0.9,
duty_cycle_period=1000,
data_format=IMAGE_DATA_FORMAT,
name=None,
**kwargs,
):
super(KWinners2d, self).__init__(
percent_on=percent_on,
k_inference_factor=k_inference_factor,
boost_strength=boost_strength,
boost_strength_factor=boost_strength_factor,
duty_cycle_period=duty_cycle_period,
name=name,
**kwargs,
)
self.data_format = data_format
if self.data_format == "channels_first":
# (batch, channels, height, width)
self.channel_axis = 1
self.height_axis = 2
self.width_axis = 3
else:
# (batch, height, width, channels)
self.height_axis = 1
self.width_axis = 2
self.channel_axis = 3
# Not know until `build`
self.channels = None
self.scale_factor = None
[docs] def build(self, input_shape):
super(KWinners2d, self).build(input_shape=input_shape)
self.channels = input_shape[self.channel_axis]
duty_cycles_shape = [1] * 4
duty_cycles_shape[self.channel_axis] = self.channels
self.duty_cycles = self.add_variable(
name="duty_cycles",
shape=duty_cycles_shape,
initializer=tf.zeros_initializer,
trainable=False,
dtype=tf.float32,
)
self.n = int(np.prod(input_shape[1:]))
self.k = int(round(self.n * self.percent_on))
self.k_inference = int(round(self.k * self.k_inference_factor))
shape = input_shape.as_list()
del shape[self.channel_axis] # Remove channel dim
del shape[0] # Remove batch dim
self.scale_factor = float(np.prod(shape))
[docs] def get_config(self):
config = {"data_format": self.data_format}
config.update(super(KWinners2d, self).get_config())
return config
[docs] def compute_duty_cycle(self, x):
batch_size = K.shape(x)[0]
learning_iterations = self.learning_iterations + batch_size
period = tf.minimum(self.duty_cycle_period, learning_iterations)
# Scale all dims but the channel dim
axis = [0, self.height_axis, self.width_axis]
count = tf.reduce_sum(tf.cast(x > 0, tf.float32), axis=axis) / self.scale_factor
duty_cycles = self.duty_cycles * tf.cast(period - batch_size, tf.float32)
# Flatten and add sum
duty_cycles = tf.reshape(duty_cycles, [-1]) + count
# Restore duty_cycles shape before dividing
duty_cycles = tf.reshape(duty_cycles, self.duty_cycles.shape)
return duty_cycles / tf.cast(period, tf.float32)
[docs] def call(self, inputs, training=None, **kwargs):
inputs = super().call(inputs, **kwargs)
k = K.in_test_phase(x=self.k_inference, alt=self.k, training=training)
kwinners = compute_kwinners(
x=inputs,
k=k,
duty_cycles=self.duty_cycles,
boost_strength=self.boost_strength,
)
duty_cycles = K.in_train_phase(
lambda: self.compute_duty_cycle(kwinners),
self.duty_cycles,
training=training,
)
self.add_update(self.duty_cycles.assign(duty_cycles, read_value=False))
increment = K.in_train_phase(K.shape(inputs)[0], 0, training=training)
self.add_update(
self.learning_iterations.assign_add(increment, read_value=False)
)
return kwinners
[docs]class KWinners(KWinnersBase):
"""Applies K-Winner function to the input tensor.
:param percent_on:
The activity of the top k = percent_on * n will be allowed to remain, the
rest are set to zero.
:type percent_on: float
:param k_inference_factor:
During inference (training=False) we increase percent_on by this factor.
percent_on * k_inference_factor must be strictly less than 1.0, ideally much
lower than 1.0
:type k_inference_factor: float
:param boost_strength:
boost strength (0.0 implies no boosting).
:type boost_strength: float
:param boost_strength_factor:
Boost strength factor to use [0..1]
:type boost_strength_factor: float
:param duty_cycle_period:
The period used to calculate duty cycles
:type duty_cycle_period: int
:param kwargs:
Additional args passed to :class:`keras.layers.Layer`
:type kwargs: dict
"""
def __init__(
self,
percent_on,
k_inference_factor=1.0,
boost_strength=1.0,
boost_strength_factor=1.0,
duty_cycle_period=1000,
name=None,
**kwargs,
):
super(KWinners, self).__init__(
percent_on=percent_on,
k_inference_factor=k_inference_factor,
boost_strength=boost_strength,
boost_strength_factor=boost_strength_factor,
duty_cycle_period=duty_cycle_period,
name=name,
**kwargs,
)
[docs] def build(self, input_shape):
super(KWinners, self).build(input_shape=input_shape)
self.n = int(input_shape[-1])
self.k = int(round(self.n * self.percent_on))
self.k_inference = int(round(self.k * self.k_inference_factor))
self.duty_cycles = self.add_variable(
name="duty_cycles",
shape=[self.n],
initializer=tf.zeros_initializer,
trainable=False,
dtype=tf.float32,
)
[docs] def compute_duty_cycle(self, inputs):
r"""
.. math::
dutyCycle = \frac{dutyCycle \times \left( period - batchSize \right)
+ newValue}{period}
"""
batch_size = tf.shape(inputs)[0]
learning_iterations = self.learning_iterations + batch_size
period = tf.minimum(self.duty_cycle_period, learning_iterations)
count = tf.reduce_sum(tf.cast(inputs > 0, tf.float32), axis=0)
result = self.duty_cycles * tf.cast(period - batch_size, tf.float32) + count
return result / tf.cast(period, tf.float32)
[docs] def call(self, inputs, training=None, **kwargs):
inputs = super().call(inputs, **kwargs)
k = K.in_test_phase(x=self.k_inference, alt=self.k, training=training)
kwinners = compute_kwinners(
x=inputs,
k=k,
duty_cycles=self.duty_cycles,
boost_strength=K.get_value(self.boost_strength),
)
duty_cycles = K.in_train_phase(
lambda: self.compute_duty_cycle(kwinners),
self.duty_cycles,
training=training,
)
self.add_update(self.duty_cycles.assign(duty_cycles, read_value=False))
increment = K.in_train_phase(K.shape(inputs)[0], 0, training=training)
self.add_update(
self.learning_iterations.assign_add(increment, read_value=False)
)
return kwinners
