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In the test_step method, we evaluate the student model on the provided dataset. |
class Distiller(keras.Model): |
def __init__(self, student, teacher): |
super(Distiller, self).__init__() |
self.teacher = teacher |
self.student = student |
def compile( |
self, |
optimizer, |
metrics, |
student_loss_fn, |
distillation_loss_fn, |
alpha=0.1, |
temperature=3, |
): |
\"\"\" Configure the distiller. |
Args: |
optimizer: Keras optimizer for the student weights |
metrics: Keras metrics for evaluation |
student_loss_fn: Loss function of difference between student |
predictions and ground-truth |
distillation_loss_fn: Loss function of difference between soft |
student predictions and soft teacher predictions |
alpha: weight to student_loss_fn and 1-alpha to distillation_loss_fn |
temperature: Temperature for softening probability distributions. |
Larger temperature gives softer distributions. |
\"\"\" |
super(Distiller, self).compile(optimizer=optimizer, metrics=metrics) |
self.student_loss_fn = student_loss_fn |
self.distillation_loss_fn = distillation_loss_fn |
self.alpha = alpha |
self.temperature = temperature |
def train_step(self, data): |
# Unpack data |
x, y = data |
# Forward pass of teacher |
teacher_predictions = self.teacher(x, training=False) |
with tf.GradientTape() as tape: |
# Forward pass of student |
student_predictions = self.student(x, training=True) |
# Compute losses |
student_loss = self.student_loss_fn(y, student_predictions) |
distillation_loss = self.distillation_loss_fn( |
tf.nn.softmax(teacher_predictions / self.temperature, axis=1), |
tf.nn.softmax(student_predictions / self.temperature, axis=1), |
) |
loss = self.alpha * student_loss + (1 - self.alpha) * distillation_loss |
# Compute gradients |
trainable_vars = self.student.trainable_variables |
gradients = tape.gradient(loss, trainable_vars) |
# Update weights |
self.optimizer.apply_gradients(zip(gradients, trainable_vars)) |
# Update the metrics configured in `compile()`. |
self.compiled_metrics.update_state(y, student_predictions) |
# Return a dict of performance |
results = {m.name: m.result() for m in self.metrics} |
results.update( |
{\"student_loss\": student_loss, \"distillation_loss\": distillation_loss} |
) |
return results |
def test_step(self, data): |
# Unpack the data |
x, y = data |
# Compute predictions |
y_prediction = self.student(x, training=False) |
# Calculate the loss |
student_loss = self.student_loss_fn(y, y_prediction) |
# Update the metrics. |
self.compiled_metrics.update_state(y, y_prediction) |
# Return a dict of performance |
results = {m.name: m.result() for m in self.metrics} |
results.update({\"student_loss\": student_loss}) |
return results |
Create student and teacher models |
Initialy, we create a teacher model and a smaller student model. Both models are convolutional neural networks and created using Sequential(), but could be any Keras model. |
# Create the teacher |
teacher = keras.Sequential( |
[ |
keras.Input(shape=(28, 28, 1)), |
layers.Conv2D(256, (3, 3), strides=(2, 2), padding=\"same\"), |
layers.LeakyReLU(alpha=0.2), |
layers.MaxPooling2D(pool_size=(2, 2), strides=(1, 1), padding=\"same\"), |
layers.Conv2D(512, (3, 3), strides=(2, 2), padding=\"same\"), |
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