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Constraining the parameters of a neural network has been shown to be beneficial in training because of the underlying regularization effects. Often, parameters are constrained via a soft penalty (which never guarantees the constraint satisfaction) or via a projection operation (which is computationally expensive). Conditional gradient (CG) optimizer, on the other hand, enforces the constraints strictly without the need for an expensive projection step. It works by minimizing a linear approximation of the objective within the constraint set. In this notebook, we demonstrate the appliction of Frobenius norm constraint via the CG optimizer on the MNIST dataset. CG is now available as a tensorflow API. More details of the optimizer are available at https://arxiv.org/pdf/1803.06453.pdf
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import tensorflow as tf
import tensorflow_addons as tfa
from matplotlib import pyplot as plt
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# Hyperparameters
batch_size=64
epochs=10
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model_1 = tf.keras.Sequential([
tf.keras.layers.Dense(64, input_shape=(784,), activation='relu', name='dense_1'),
tf.keras.layers.Dense(64, activation='relu', name='dense_2'),
tf.keras.layers.Dense(10, activation='softmax', name='predictions'),
])
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# Load MNIST dataset as NumPy arrays
dataset = {}
num_validation = 10000
(x_train, y_train), (x_test, y_test) = tf.keras.datasets.mnist.load_data()
# Preprocess the data
x_train = x_train.reshape(-1, 784).astype('float32') / 255
x_test = x_test.reshape(-1, 784).astype('float32') / 255
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def frobenius_norm(m):
"""This function is to calculate the frobenius norm of the matrix of all
layer's weight.
Args:
m: is a list of weights param for each layers.
"""
total_reduce_sum = 0
for i in range(len(m)):
total_reduce_sum = total_reduce_sum + tf.math.reduce_sum(m[i]**2)
norm = total_reduce_sum**0.5
return norm
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CG_frobenius_norm_of_weight = []
CG_get_weight_norm = tf.keras.callbacks.LambdaCallback(
on_epoch_end=lambda batch, logs: CG_frobenius_norm_of_weight.append(
frobenius_norm(model_1.trainable_weights).numpy()))
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# Compile the model
model_1.compile(
optimizer=tfa.optimizers.ConditionalGradient(
learning_rate=0.99949, lambda_=203), # Utilize TFA optimizer
loss=tf.keras.losses.SparseCategoricalCrossentropy(),
metrics=['accuracy'])
history_cg = model_1.fit(
x_train,
y_train,
batch_size=batch_size,
validation_data=(x_test, y_test),
epochs=epochs,
callbacks=[CG_get_weight_norm])
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model_2 = tf.keras.Sequential([
tf.keras.layers.Dense(64, input_shape=(784,), activation='relu', name='dense_1'),
tf.keras.layers.Dense(64, activation='relu', name='dense_2'),
tf.keras.layers.Dense(10, activation='softmax', name='predictions'),
])
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SGD_frobenius_norm_of_weight = []
SGD_get_weight_norm = tf.keras.callbacks.LambdaCallback(
on_epoch_end=lambda batch, logs: SGD_frobenius_norm_of_weight.append(
frobenius_norm(model_2.trainable_weights).numpy()))
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# Compile the model
model_2.compile(
optimizer=tf.keras.optimizers.SGD(0.01), # Utilize SGD optimizer
loss=tf.keras.losses.SparseCategoricalCrossentropy(),
metrics=['accuracy'])
history_sgd = model_2.fit(
x_train,
y_train,
batch_size=batch_size,
validation_data=(x_test, y_test),
epochs=epochs,
callbacks=[SGD_get_weight_norm])
The current implementation of CG optimizer is based on Frobenius Norm, with considering Frobenius Norm as regularizer in the target function. Therefore, we compare CG’s regularized effect with SGD optimizer, which has not imposed Frobenius Norm regularizer.
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plt.plot(
CG_frobenius_norm_of_weight,
color='r',
label='CG_frobenius_norm_of_weights')
plt.plot(
SGD_frobenius_norm_of_weight,
color='b',
label='SGD_frobenius_norm_of_weights')
plt.xlabel('Epoch')
plt.ylabel('Frobenius norm of weights')
plt.legend(loc=1)
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plt.plot(history_cg.history['accuracy'], color='r', label='CG_train')
plt.plot(history_cg.history['val_accuracy'], color='g', label='CG_test')
plt.plot(history_sgd.history['accuracy'], color='pink', label='SGD_train')
plt.plot(history_sgd.history['val_accuracy'], color='b', label='SGD_test')
plt.xlabel('Epoch')
plt.ylabel('Accuracy')
plt.legend(loc=4)
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