Concat Layer

• Layer type: Concat
• Doxygen Documentation
• Header: ./include/caffe/layers/concat_layer.hpp
• CPU implementation: ./src/caffe/layers/concat_layer.cpp
• CUDA GPU implementation: ./src/caffe/layers/concat_layer.cu
• Input
  • n_i * c_i * h * w for each input blob i from 1 to K.
• Output
  • if axis = 0: (n_1 + n_2 + ... + n_K) * c_1 * h * w, and all input c_i should be the same.
  • if axis = 1: n_1 * (c_1 + c_2 + ... + c_K) * h * w, and all input n_i should be the same.

• Sample

  layer {
    name: "concat"
    bottom: "in1"
    bottom: "in2"
    top: "out"
    type: "Concat"
    concat_param {
      axis: 1
    }
  }
  

The Concat layer is a utility layer that concatenates its multiple input blobs to one single output blob.

Parameters

• Parameters (ConcatParameter concat_param)
  • Optional
    • axis [default 1]: 0 for concatenation along num and 1 for channels.
• From ./src/caffe/proto/caffe.proto):

message ConcatParameter {
  // The axis along which to concatenate -- may be negative to index from the
  // end (e.g., -1 for the last axis).  Other axes must have the
  // same dimension for all the bottom blobs.
  // By default, ConcatLayer concatenates blobs along the "channels" axis (1).
  optional int32 axis = 2 [default = 1];

  // DEPRECATED: alias for "axis" -- does not support negative indexing.
  optional uint32 concat_dim = 1 [default = 1];
}