Recurrent Neural Networks
References
<https://d396qusza40orc.cloudfront.net/neuralnets/lecture_slides/lec7.pdf> (coursera hinton)
<http://karpathy.github.io/2015/05/21/rnn-effectiveness/>
<http://colah.github.io/posts/2015-08-Understanding-LSTMs>
<http://www.wildml.com/2015/09/recurrent-neural-networks-tutorial-part-1-introduction-to-rnns>
<https://en.wikipedia.org/wiki/Recurrent_neural_network>
<https://www.willamette.edu/~gorr/classes/cs449/rnn1.html>
<http://www.deeplearningbook.org/contents/rnn.html>
<http://cs224d.stanford.edu/> (socher class on deep learning for nlp)