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Creates a grad-pass-through op with the forward behavior provided in f.

Use this function to wrap any op, maintaining its behavior in the forward pass, but replacing the original op in the backward graph with an identity. For example:

x = tf.Variable(1.0, name="x")
z = tf.Variable(3.0, name="z")

with tf.GradientTape() as tape:
  # y will evaluate to 9.0
  y = tf.grad_pass_through(x.assign)(z**2)
# grads will evaluate to 6.0
grads = tape.gradient(y, z)

Another example is a 'differentiable' moving average approximation, where gradients are allowed to flow into the last value fed to the moving average, but the moving average is still used for the forward pass:

x = ... # Some scalar value
# A moving average object, we don't need to know how this is implemented
moving_average = MovingAverage()
with backprop.GradientTape() as tape:
  # mavg_x will evaluate to the current running average value
  mavg_x = tf.grad_pass_through(moving_average)(x)
grads = tape.gradient(mavg_x, x) # grads will evaluate to 1.0

f function f(*x) that returns a Tensor or nested structure of Tensor outputs.

A function h(x) which returns the same values as f(x) and whose gradients are the same as those of an identity function.