caffe中的concate层

concate 默认使用axis = 0，按照num拼接；

简单介绍

主要函数

1.LayerSetUp 函数：

template <typename Dtype>void ConcatLayer<Dtype>::LayerSetUp(const vector<Blob<Dtype>*>& bottom,      const vector<Blob<Dtype>*>& top) {  const ConcatParameter& concat_param = this->layer_param_.concat_param();  CHECK(!(concat_param.has_axis() && concat_param.has_concat_dim()))      << "Either axis or concat_dim should be specified; not both.";}//axis ，dim ：0 为 num 维度链接，1 为 channel 维度链接
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2.Reshape 函数：

template <typename Dtype>void ConcatLayer<Dtype>::Reshape(const vector<Blob<Dtype>*>& bottom,      const vector<Blob<Dtype>*>& top) {  const int num_axes = bottom[0]->num_axes();  const ConcatParameter& concat_param = this->layer_param_.concat_param();  if (concat_param.has_concat_dim()) {    concat_axis_ = static_cast<int>(concat_param.concat_dim());    // Don't allow negative indexing for concat_dim, a uint32 -- almost    // certainly unintended.    CHECK_GE(concat_axis_, 0) << "casting concat_dim from uint32 to int32 "        << "produced negative result; concat_dim must satisfy "        << "0 <= concat_dim < " << kMaxBlobAxes;    CHECK_LT(concat_axis_, num_axes) << "concat_dim out of range.";  } else {    concat_axis_ = bottom[0]->CanonicalAxisIndex(concat_param.axis());  }  // Initialize with the first blob.  blob: num x channel x height x width  vector<int> top_shape = bottom[0]->shape();  num_concats_ = bottom[0]->count(0, concat_axis_);  //concat_axis_ = 0 : num_concats_=num;concat_axis_ = 1 : num_concats_=num x channel;  concat_input_size_ = bottom[0]->count(concat_axis_ + 1);  //concat_axis_ = 0 : concat_input_size_=channel x height x width;  //concat_axis_ = 1 : num_concats_=height x width;  int bottom_count_sum = bottom[0]->count();  for (int i = 1; i < bottom.size(); ++i) {    CHECK_EQ(num_axes, bottom[i]->num_axes())        << "All inputs must have the same #axes.";    for (int j = 0; j < num_axes; ++j) {      if (j == concat_axis_) { continue; }      CHECK_EQ(top_shape[j], bottom[i]->shape(j))          << "All inputs must have the same shape, except at concat_axis.";    }    bottom_count_sum += bottom[i]->count();    top_shape[concat_axis_] += bottom[i]->shape(concat_axis_);  }  top[0]->Reshape(top_shape);  CHECK_EQ(bottom_count_sum, top[0]->count());}
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3.Forward_cpu 函数：

template <typename Dtype>void ConcatLayer<Dtype>::Forward_cpu(const vector<Blob<Dtype>*>& bottom,      const vector<Blob<Dtype>*>& top) {  Dtype* top_data = top[0]->mutable_cpu_data();  int offset_concat_axis = 0;  const int top_concat_axis = top[0]->shape(concat_axis_);  for (int i = 0; i < bottom.size(); ++i) {//遍历所有输入bottom    const Dtype* bottom_data = bottom[i]->cpu_data();    const int bottom_concat_axis = bottom[i]->shape(concat_axis_);    for (int n = 0; n < num_concats_; ++n) {      caffe_copy(bottom_concat_axis * concat_input_size_,          //case 0：num x channel x h x w;case 1: channel x h x w          bottom_data + n * bottom_concat_axis * concat_input_size_,          //case 0：bottom_data + n x num x channel x h x w ;          //case 1:bottom_data + n x channel x h x w ;          top_data + (n * top_concat_axis + offset_concat_axis)              * concat_input_size_);    }//把 各个bottom data 拷贝到输出 top data 的对应位置    offset_concat_axis += bottom_concat_axis;  }}
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4. Backward_cpu 函数：

template <typename Dtype>void ConcatLayer<Dtype>::Backward_cpu(const vector<Blob<Dtype>*>& top,      const vector<bool>& propagate_down, const vector<Blob<Dtype>*>& bottom) {  const Dtype* top_diff = top[0]->cpu_diff();  int offset_concat_axis = 0;  const int top_concat_axis = top[0]->shape(concat_axis_);  for (int i = 0; i < bottom.size(); ++i) {    if (!propagate_down[i]) { continue; }    Dtype* bottom_diff = bottom[i]->mutable_cpu_diff();    const int bottom_concat_axis = bottom[i]->shape(concat_axis_);    for (int n = 0; n < num_concats_; ++n) {      caffe_copy(bottom_concat_axis * concat_input_size_, top_diff +          (n * top_concat_axis + offset_concat_axis) * concat_input_size_,          bottom_diff + n * bottom_concat_axis * concat_input_size_);    }    offset_concat_axis += bottom_concat_axis;  }//对 diff 做和data相同的链接}