Gradient not defined for flip()?

[samuelkim16]

When I use numpy.flip in my function that I would like to take the gradient of, I get the below error

NotImplementedError: VJP of flip wrt argnums (0,) not defined

which I assume means the gradient of flip is not defined. Is there a particular reason this is the case?

[xiaozhongguo]

numpy.flip - Reverse the order of elements in an array along the given axis. it's nothing to do with the elements.