new function to support LSTM Unit

include/NeuralNetwork/ActivationFunction/Linear.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "./ActivationFunction.h"
+
+namespace NeuralNetwork {
+namespace ActivationFunction {
+
+	class Linear: public ActivationFunction {
+		public:
+			Linear(const float &lambdaP=1.0): lambda(lambdaP) {}
+			inline virtual float derivatedOutput(const float &,const float &) override { return lambda;  }
+			inline virtual float operator()(const float &x) override { return x*lambda; };
+
+			virtual ActivationFunction* clone() const override {
+				return new Linear(lambda);
+			}
+
+			virtual std::string stringify() const override {
+				return "{ \"class\": \"NeuralNetwork::ActivationFunction::Linear\", \"lamba\" : "+std::to_string(lambda)+"}";
+			}
+
+		protected:
+			float lambda;
+	};
+}
+}