吴裕雄--天生自然TensorFlow2教程：链式法则

import tensorflow as tf

x = tf.constant(1.)
w1 = tf.constant(2.)
b1 = tf.constant(1.)
w2 = tf.constant(2.)
b2 = tf.constant(1.)

with tf.GradientTape(persistent=True) as tape:
    tape.watch([w1, b1, w2, b2])
    y1 = x * w1 + b1
    y2 = y1 * w2 + b2

dy2_dy1 = tape.gradient(y2, [y1])[0]
dy1_dw1 = tape.gradient(y1, [w1])[0]
dy2_dw1 = tape.gradient(y2, [w1])[0]

dy2_dy1 * dy1_dw1

dy2_dw1