In this chapter, we introduced lots of new and complex material. We became familiar with the limitations of value iteration in complex environments with large observation spaces and discussed how to overcome them with Q-learning. We checked the Q-learning algorithm on the FrozenLake environment and discussed the approximation of Q-values with neural networks and the extra complications that arise from this approximation. We covered several tricks for DQNs to improve their training stability and convergence, such as experience replay buffer, target networks, and frame stacking. Finally, we combined those extensions in to one single implementation of DQN that solves the Pong environment from the Atari games suite.

In the next chapter, we'll look at a set of tricks that researchers have found, since 2015, to improve DQN convergence and quality, which (combined) can produce state-of-the-art results on most of the 54 Atari games. This set was published in 2017 and we'll analyze and reimplement...