遞歸神經網路(Recurrent Neural Network): Back-propagation Through Time

https://medium.com/@chih.sheng.huang821/%E9%81%9E%E6%AD%B8%E7%A5%9E%E7%B6%93%E7%B6%B2%E8%B7%AF-recurrent-neural-network-back-propagation-through-time-8d49ebf04b77