https://github.com/HIPS/autograd/blob/master/docs/tutorial.md
https://www.youtube.com/watch?v=Q_9ZpoCQkDE
http://www.cs.toronto.edu/~rgrosse/courses/csc321_2017/tutorials/tut4.pdf
https://www.youtube.com/watch?v=ma2KXWblllc
https://pytorch.org/docs/stable/autograd.html
https://pytorch.org/tutorials/beginner/blitz/autograd_tutorial.html#gradients
https://github.com/jcjohnson/pytorch-examples/tree/master/autograd