[ML] Constant function.

MathLib/ConstantFunction.h

+/**
+ * \author Norihiro Watanabe
+ * \date   2013-08-13
+ *
+ * \copyright
+ * Copyright (c) 2012-2015, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ *
+ */
+
+#ifndef MATHLIB_CONSTANTFUNCTION_H_
+#define MATHLIB_CONSTANTFUNCTION_H_
+
+#include <array>
+#include <numeric>
+
+namespace MathLib
+{
+
+/**
+ * A constant function.
+ * \f[
+ * 	f(x_1,...,x_k)=a_0
+ * \f]
+ */
+template <typename T_TYPE>
+class ConstantFunction
+{
+public:
+	explicit ConstantFunction(T_TYPE const& value)
+	: _value(value)
+	{}
+
+	T_TYPE operator()() const
+	{
+		return _value;
+	}
+private:
+	T_TYPE const _value;
+};
+
+}
+
+#endif  // MATHLIB_CONSTANTFUNCTION_H_