Caffe define a new layer hands on

Here's roughly the process I follow.

1. Add a class declaration for your layer to the appropriate one of common_layers.hpp,data_layers.hpp, loss_layers.hpp, neuron_layers.hpp, orvision_layers.hpp. Include an inline implementation of type and the *Blobs()methods to specify blob number requirements. Omit the *_gpu declarations if you'll only be implementing CPU code.
2. Implement your layer in layers/your_layer.cpp.
   • SetUp for initialization: reading parameters, allocating buffers, etc.
   • Forward_cpu for the function your layer computes
   • Backward_cpu for its gradient
3. (Optional) Implement the GPU versions Forward_gpu and Backward_gpu inlayers/your_layer.cu.
4. Add your layer to proto/caffe.proto, updating the next available ID. Also declare parameters, if needed, in this file.
5. Make your layer createable by adding it to layer_factory.cpp.
6. Write tests in test/test_your_layer.cpp. Usetest/test_gradient_check_util.hpp to check that your Forward and Backward implementations are in numerical agreement.