f'(y) = B / (x * x + 1)
public void DerivativeTest() { double[] expected = { 0.31831, 0.315158, 0.306067, 0.292027, 0.274405, 0.254648, 0.234051, 0.213631, 0.194091, 0.175862, 0.159155 }; CauchitLinkFunction target = new CauchitLinkFunction(); for (int i = 0; i < 11; i++) { double x = i / 10.0; double y = target.Inverse(x); double d1 = target.Derivative(x); double d2 = target.Derivative2(y); Assert.AreEqual(expected[i], d1, 1e-6); Assert.AreEqual(expected[i], d2, 1e-6); Assert.IsFalse(Double.IsNaN(d1)); Assert.IsFalse(Double.IsNaN(d2)); } }