public void TestSecondPartial(double[] arr, double[] expected) { Derivative = new Derivative(TypicalMultivariateFunction); var vector = new Vector(arr); var joinedResult = new double[4]; for (int i = 0; i < 2; i++) { for (int j = 0; j < 2; j++) { joinedResult[2 * i + j] = Derivative.GetSecondPartialDerivative(vector, i, j); } } Assert.AreEqual(expected, joinedResult); }