Neural Network 적용 전에 Input data를 Normalize 해야 하는 이유

학습을 더 빠르게 도와줌

https://www.coursera.org/learn/machine-learning/lecture/xx3Da/gradient-descent-in-practice-i-feature-scaling

https://stackoverflow.com/questions/4674623/why-do-we-have-to-normalize-the-input-for-an-artificial-neural-network

http://goodtogreate.tistory.com/entry/Neural-Network-%EC%A0%81%EC%9A%A9-%EC%A0%84%EC%97%90-Input-data%EB%A5%BC-Normalize-%ED%95%B4%EC%95%BC-%ED%95%98%EB%8A%94-%EC%9D%B4%EC%9C%A0