I wanted to share this preprint of a Review of automatic differentiation and its efficient implementation. You can access the article on arXiv, see https://arxiv.org/abs/1811.05031
As you may know, automatic differentiation plays a critical role in Stan, as it allows us to compute the gradient of the posterior distribution. I think the article will be of interest to those who want to crack the black box open – either to become better practitioners or simply out of curiosity.