Encog.Engine.Network.Activation.ActivationSIN.DerivativeFunction C# (CSharp) Method

        public virtual double DerivativeFunction(double b, double a)
        {
            return BoundMath.Cos(b);
        }

        public void TestSIN()
        {
            var activation = new ActivationSIN();

            Assert.IsTrue(activation.HasDerivative);

            var clone = activation.Clone();

            Assert.IsInstanceOfType(clone, typeof(ActivationSIN));

            double[] input = { 0.0, Math.PI / 4, Math.PI / 2 };

            activation.ActivationFunction(input, 0, 3); //it's actually Sin(2x)

            Assert.AreEqual(0.0, input[0], 0.01);
            Assert.AreEqual(1.0, input[1], 0.01);
            Assert.AreEqual(0.0, input[2], 0.01);

            // test derivative
            input[0] = activation.DerivativeFunction(0, input[0]);
            input[1] = activation.DerivativeFunction(Math.PI / 4, input[1]);
            input[2] = activation.DerivativeFunction(Math.PI / 2, input[2]);
            Assert.AreEqual(1.0, input[0], 0.01);
            Assert.AreEqual(0.0, input[1], 0.01);
            Assert.AreEqual(-1.0, input[2], 0.01);
        }