Sigmoid function -- 'S' shaped function

With this post, we are starting the third Chapter -- Activation functions and their derivatives. How they are used in Deep Learning will be discussed later. The most important post in this chapter is the last one where we will talk about the Softmax activation function and its Jacobian which very few people talk about. These posts are very short. So, let us begin with the first Activation function, i.e., the Sigmoid function.