new function to support LSTM Unit

include/NeuralNetwork/BasisFunction/Product.h

@@ -0,0 +1,34 @@
+#pragma once
+
+#include "./BasisFunction.h"
+
+namespace NeuralNetwork {
+namespace BasisFunction {
+
+	class Product: public BasisFunction {
+		public:
+			Product() {}
+
+			/**
+			 * @brief function computes product of inputs, where weight > 0.5
+			 */
+			inline virtual float operator()(const std::vector<float>& weights, const std::vector<float>& input) const override {
+				float product=1.0;
+				for(size_t i=0;i<weights.size();i++) {
+					if(weights[i] > 0.5)
+						product=product*input[i];
+				}
+				return product;
+			}
+
+			virtual Product* clone() const override {
+				return new Product();
+			}
+
+			virtual std::string stringify() const override {
+				return "{ \"class\": \"NeuralNetwork::BasisFunction::Product\" }";
+			}
+
+	};
+}
+}