https://indico.cern.ch/event/708041/contributions/3308814/attachments/1813852/2963725/automatic_differentiation_and_deep_learning.pdf
https://pytorch.org/docs/stable/notes/autograd.html#complex-autograd-doc
Recommended: shows why the backprop is formally expressed with the Jacobian
https://cs.ubc.ca/~fwood/CS340/lectures/AD1.pdf
