add LinearFunction in MathLib

MathLib/LinearFunction.h

+/**
+ * \author Norihiro Watanabe
+ * \date   2013-08-13
+ *
+ * \copyright
+ * Copyright (c) 2013, 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 LINEARFUNCTION_H_
+#define LINEARFUNCTION_H_
+
+#include <array>
+#include <algorithm>
+#include <cassert>
+
+namespace MathLib
+{
+
+/**
+ * Linear function
+ * \f[
+ * 	f(x_1,...,x_k)=a_0+a_1*x_1+...+a_k*x_k
+ * \f]
+ *
+ * \tparam T_TYPE  value type
+ * \tparam N_VARS  the number of variables (k)
+ */
+template <typename T_TYPE, unsigned N_VARS>
+class LinearFunction
+{
+public:
+	/**
+	 * Constructor
+	 * \param coefficients  an array of coefficients of a linear function.
+	 * The size of the coefficient array should equal to the number of variables + 1
+	 */
+	explicit LinearFunction(const T_TYPE* coefficients)
+	: _coefficients(copy(coefficients))
+	{
+		static_assert(N_VARS>0, "Template parameter N_VARS in LinearFunction should be nonzero");
+	}
+
+	/**
+	 * evaluate the function
+	 * \param x  an array of variables. the size of the array should equal to the number of variables + 1
+	 */
+	T_TYPE operator()(T_TYPE const * const x) const
+	{
+		T_TYPE v = _coefficients[0];
+		for (unsigned i=0; i<N_VARS; i++)
+			v += _coefficients[i+1]*x[i];
+		return v;
+	}
+
+private:
+	/// copy a given raw array to std::array
+	static std::array<T_TYPE, N_VARS+1> copy(const T_TYPE* coefficients)
+	{
+		std::array<T_TYPE, N_VARS+1> temp;
+		std::copy(coefficients, coefficients+ temp.size(), temp.data());
+		return temp;
+	}
+
+	/// Coefficients of a linear function
+	const std::array<T_TYPE, N_VARS+1> _coefficients;
+};
+
+} // MathLib
+
+#endif /* LINEARFUNCTION_H_ */