勾配降下法
https://teratail.com/questions/72127
http://www.mwsoft.jp/programming/equation/gradient_descent.html
http://shironeko.hateblo.jp/entry/2016/10/29/173634
CNN
https://qiita.com/taigamikami/items/7d915615d1478e19f133
CNNで文章を分類する方法
http://tkengo.github.io/blog/2016/03/11/understanding-convolutional-neural-networks-for-nlp/
padding
https://qiita.com/tadOne/items/48302a399dcad44c69c8
tf.InteractiveSession()
http://seishin55.hatenablog.com/entry/2017/04/23/155707