Directional Derivative and its relation to Gradient Vector

Understanding Directional Derivative is the doorway from Mathematics to enter into the world of machine learning. In the entire machine learning world, we talk about updating weights and parameters using Gradient Descent or its super and state-of-the-art version which takes computers to train and get optimum parameters days of time.
Understanding Machine Learning from Mathematical point of view is fun, satisfying and innovative approach to solve novel problems of AI.