compile error when using customize layer which only implement CPU function

[吳思明]

I'm using 

Ubuntu 16.0 

Cuda 8.0 

cudnn 5.1

gtx1070

I want to mirror Image in caffe so I write mirror_layer myself

It did well on Windows7 but failed on Ubuntu 16.0

the error messege said

undefined reference to Forward_gpu and Backward_gpu

I didn't implement these two function because I don't know how to write them

And I believe it can work, or am I wrong?

Hope someone using customize layer with only cpu function can help me.

I don't know how to write Python so using Python Layer is my final solution.

Thanks.