python - 为什么 tf.gradients 不适用于整数常量？

Question

为什么下面的函数打印 None？

a = tf.constant(4)
b = tf.constant(2)

gr = tf.gradients(a + b, [a, b])

print(sess.run(gr))

但是当我改变

-a = tf.constant(4)
-b = tf.constant(2)
+a = tf.constant(4.0)
+b = tf.constant(2.0)

它打印渐变。这是什么原因？

Answer 1

根据https://github.com/tensorflow/tensorflow/issues/20524由于这个原因，tensorflow 团队使 tf.gradients 与整数张量不兼容:

In effect, allowing gradients on integer tensors was causing incorrectness in tf.while_loop, and there was no satisfactory way to resolve them without this change.