Gradient
激活函数及梯度
sigmoid
tanh
relu
损失函数及梯度
链式法则
函数优化
Himmelblau函数优化
手写数字问题
import tensorflow as tf
from tensorflow import keras
from tensorflow.keras import datasets, layers, optimizers, Sequential, metrics
import os
os.environ['TF_CPP_MIN_LOG_LEVEL'] = '2'
def preprocess(x, y):
x = tf.cast(x, dtype=tf.float32) / 255.
y = tf.cast(y, dtype=tf.int32)
return x,y
(x, y), (x_test, y_test) = datasets.fashion_mnist.load_data()
print(x.shape, y.shape)
batchsz = 128
db = tf.data.Dataset.from_tensor_slices((x,y))
db = db.map(preprocess).shuffle(10000).batch(batchsz)
db_test = tf.data.Dataset.from_tensor_slices((x_test,y_test))
db_test = db_test.map(preprocess).batch(batchsz)
db_iter = iter(db)
sample = next(db_iter)
print('batch:', sample[0].shape, sample[1].shape)
model = Sequential([
layers.Dense(256, activation=tf.nn.relu), # [b, 784] => [b, 256]
layers.Dense(128, activation=tf.nn.relu), # [b, 256] => [b, 128]
layers.Dense(64, activation=tf.nn.relu), # [b, 128] => [b, 64]
layers.Dense(32, activation=tf.nn.relu), # [b, 64] => [b, 32]
layers.Dense(10) # [b, 32] => [b, 10], 330 = 32*10 + 10
])
model.build(input_shape=[None, 28*28])
model.summary()
# w = w - lr*grad
optimizer = optimizers.Adam(lr=1e-3)
def main():
for epoch in range(30):
for step, (x,y) in enumerate(db):
# x: [b, 28, 28] => [b, 784]
# y: [b]
x = tf.reshape(x, [-1, 28*28])
with tf.GradientTape() as tape:
# [b, 784] => [b, 10]
logits = model(x)
y_onehot = tf.one_hot(y, depth=10)
# [b]
loss_mse = tf.reduce_mean(tf.losses.MSE(y_onehot, logits))
loss_ce = tf.losses.categorical_crossentropy(y_onehot, logits, from_logits=True)
loss_ce = tf.reduce_mean(loss_ce)
grads = tape.gradient(loss_ce, model.trainable_variables)
optimizer.apply_gradients(zip(grads, model.trainable_variables))
if step % 100 == 0:
print(epoch, step, 'loss:', float(loss_ce), float(loss_mse))
# test
total_correct = 0
total_num = 0
for x,y in db_test:
# x: [b, 28, 28] => [b, 784]
# y: [b]
x = tf.reshape(x, [-1, 28*28])
# [b, 10]
logits = model(x)
# logits => prob, [b, 10]
prob = tf.nn.softmax(logits, axis=1)
# [b, 10] => [b], int64
pred = tf.argmax(prob, axis=1)
pred = tf.cast(pred, dtype=tf.int32)
# pred:[b]
# y: [b]
# correct: [b], True: equal, False: not equal
correct = tf.equal(pred, y)
correct = tf.reduce_sum(tf.cast(correct, dtype=tf.int32))
total_correct += int(correct)
total_num += x.shape[0]
acc = total_correct / total_num
print(epoch, 'test acc:', acc)
if __name__ == '__main__':
main()
TensorBoard可视化
visdom
Keras高层API