Automatic differentiation is a term I first heard of while working on (as it turns out now, a bit cumbersome) implementation of backpropagation algorithm – after all it caused lots of headaches as I had to handle all derivatives myself with almost pen-and-paper like approach. Obviously I made many mistakes until I got my final solution working.
At that time, I was aware some libraries like Theano or Tensorflow handle derivatives in a certain “magical” way for free. I never knew exactly what happens deep in the guts of these libraries though and I somehow suspected it is rather painful than fun to grasp (apparently, I was wrong!).
I decided to take a shot and directed my first steps towards TensorFlow official documentation to quickly find out what the magic is. The term I was looking for was automatic differentiation.