add softplus layer

Author: vera121

FEATURES.md

@@ -63,6 +63,7 @@ scaled_tanh_layer
 shape_layer  
 shuffle_channel_layer  
 sin_layer  
+softplus_layer  
 softsign_layer  
 space_to_batch_nd_layer  
 space_to_depth_layer  

include/caffe/layers/softplus_layer.hpp

@@ -0,0 +1,36 @@
+#ifndef CAFFE_SOFTPLUS_LAYER_HPP_
+#define CAFFE_SOFTPLUS_LAYER_HPP_
+
+#include <vector>
+
+#include "caffe/blob.hpp"
+#include "caffe/layer.hpp"
+#include "caffe/proto/caffe.pb.h"
+
+#include "caffe/layers/neuron_layer.hpp"
+
+namespace caffe {
+
+
+template <typename Dtype>
+class SoftplusLayer : public NeuronLayer<Dtype> {
+ public:
+  explicit SoftplusLayer(const LayerParameter& param)
+      : NeuronLayer<Dtype>(param) {}
+
+  virtual inline const char* type() const { return "Softplus"; }
+
+ protected:
+  virtual void Forward_cpu(const vector<Blob<Dtype>*>& bottom,
+      const vector<Blob<Dtype>*>& top);
+  virtual void Backward_cpu(const vector<Blob<Dtype>*>& top,
+      const vector<bool>& propagate_down, const vector<Blob<Dtype>*>& bottom) {
+    for (int i = 0; i < propagate_down.size(); ++i) {
+      if (propagate_down[i]) { NOT_IMPLEMENTED; }
+    }
+  }
+};
+
+}  // namespace caffe
+
+#endif  // CAFFE_SOFTPLUS_LAYER_HPP_

src/caffe/layers/softplus_layer.cpp

@@ -0,0 +1,23 @@
+#include <math.h>
+#include <vector>
+
+#include "caffe/layers/softplus_layer.hpp"
+
+namespace caffe {
+
+
+template <typename Dtype>
+void SoftplusLayer<Dtype>::Forward_cpu(const vector<Blob<Dtype>*>& bottom,
+    const vector<Blob<Dtype>*>& top) {
+  const Dtype* bottom_data = bottom[0]->cpu_data();
+  Dtype* top_data = top[0]->mutable_cpu_data();
+  const int count = bottom[0]->count();
+  for (int i = 0; i < count; ++i) {
+    top_data[i] = logf(expf(bottom_data[i]) + 1);
+  }
+}
+
+INSTANTIATE_CLASS(SoftplusLayer);
+REGISTER_LAYER_CLASS(Softplus);
+
+}  // namespace caffe