随机梯度下降SGD、BGD、MBGD
https://www.cnblogs.com/lliuye/p/9451903.html
https://blog.csdn.net/weixin_39445556/article/details/83543945
https://blog.csdn.net/weixin_39445556/article/details/83661219
https://blog.csdn.net/kwame211/article/details/80364079