Method Backward_cpu

src/caffe/layers/eltwise_layer.cpp:102–153

template <typename Dtype>
void EltwiseLayer<Dtype>::Backward_cpu(const vector<Blob<Dtype>*>& top,
    const vector<bool>& propagate_down, const vector<Blob<Dtype>*>& bottom) {
  const int* mask = NULL;
  const int count = top[0]->count();
  const Dtype* top_data = top[0]->cpu_data();
  const Dtype* top_diff = top[0]->cpu_diff();
  for (int i = 0; i < bottom.size(); ++i) {
    if (propagate_down[i]) {
      const Dtype* bottom_data = bottom[i]->cpu_data();
      Dtype* bottom_diff = bottom[i]->mutable_cpu_diff();
      switch (op_) {
      case EltwiseParameter_EltwiseOp_PROD:
        if (stable_prod_grad_) {
          bool initialized = false;
          for (int j = 0; j < bottom.size(); ++j) {
            if (i == j) { continue; }
            if (!initialized) {
              caffe_copy(count, bottom[j]->cpu_data(), bottom_diff);
              initialized = true;
            } else {
              caffe_mul(count, bottom[j]->cpu_data(), bottom_diff,
                        bottom_diff);
            }
          }
        } else {
          caffe_div(count, top_data, bottom_data, bottom_diff);
        }
        caffe_mul(count, bottom_diff, top_diff, bottom_diff);
        break;
      case EltwiseParameter_EltwiseOp_SUM:
        if (coeffs_[i] == Dtype(1)) {
          caffe_copy(count, top_diff, bottom_diff);
        } else {
          caffe_cpu_scale(count, coeffs_[i], top_diff, bottom_diff);
        }
        break;
      case EltwiseParameter_EltwiseOp_MAX:
        mask = max_idx_.cpu_data();
        for (int index = 0; index < count; ++index) {
          Dtype gradient = 0;
          if (mask[index] == i) {
            gradient += top_diff[index];
          }
          bottom_diff[index] = gradient;
        }
        break;
      default:
        LOG(FATAL) << "Unknown elementwise operation.";
      }
    }
  }
}

#ifdef CPU_ONLY
STUB_GPU(EltwiseLayer);