我正在尝试为“ my_op”编写一个自定义渐变函数,出于示例的原因,该函数仅包含对tf.identity()的调用(理想情况下,它可以是任何图形)。
import tensorflow as tf
from tensorflow.python.framework import function
def my_op_grad(x):
return [tf.sigmoid(x)]
@function.Defun(a=tf.float32, python_grad_func=my_op_grad)
def my_op(a):
return tf.identity(a)
a = tf.Variable(tf.constant([5., 4., 3., 2., 1.], dtype=tf.float32))
sess = tf.Session()
sess.run(tf.initialize_all_variables())
grad = tf.gradients(my_op(a), [a])[0]
result = sess.run(grad)
print(result)
sess.close()
不幸的是,我得到以下错误:
Traceback (most recent call last):
File "custom_op.py", line 19, in <module>
grad = tf.gradients(my_op(a), [a])[0]
File "/Users/njk/tfm/lib/python3.5/site-packages/tensorflow/python/framework/function.py", line 528, in __call__
return call_function(self._definition, *args, **kwargs)
File "/Users/njk/tfm/lib/python3.5/site-packages/tensorflow/python/framework/function.py", line 267, in call_function
compute_shapes=False)
File "/Users/njk/tfm/lib/python3.5/site-packages/tensorflow/python/framework/ops.py", line 2285, in create_op
raise TypeError("Input #%d is not a tensor: %s" % (idx, a))
TypeError: Input #0 is not a tensor: <tensorflow.python.ops.variables.Variable object at 0x1080d2710>
我知道可以创建自定义C ++操作,但就我而言,我只需要为该函数编写一个自定义渐变即可使用标准TensorFlow操作轻松用Python编写,因此我要避免编写不必要的C ++代码。
另外,我正在使用GitHub的TensorFlow的上游版本。
请注意,python_grad_func需要与ops.RegisterGradient(https://github.com/tensorflow/tensorflow/blob/master/tensorflow/python/framework/function.py#L349)相同的接口。
这是修改后的代码示例:
def my_op_grad(op, grad): ### instead of my_op_grad(x)
return tf.sigmoid(op.inputs[0])
@function.Defun(a=tf.float32, python_grad_func=my_op_grad)
def my_op(a):
return tf.identity(a)
def main(unused_argv):
a = tf.Variable(tf.constant([-5., 4., -3., 2., 1.], dtype=tf.float32))
sess = tf.Session()
sess.run(tf.initialize_all_variables())
a = tf.identity(a) #workaround for bug github.com/tensorflow/tensorflow/issues/3710
grad = tf.gradients(my_op(a), [a])[0]
result = sess.run(grad)
print(result)
sess.close()
输出:
[ 0.00669286 0.98201376 0.04742587 0.88079709 0.7310586 ]
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