Oleg Zabluda's blog
Wednesday, December 06, 2017
 
Mastering Chess and Shogi by Self-Play with a General Reinforcement Learning Algorithm (2017) David Silver, Thomas...
Mastering Chess and Shogi by Self-Play with a General Reinforcement Learning Algorithm (2017) David Silver, Thomas Hubert, Julian Schrittwieser, Ioannis Antonoglou, Matthew Lai, Arthur Guez, Marc Lanctot, Laurent Sifre, Dharshan Kumaran, Thore Graepel, Timothy Lillicrap, Karen Simonyan, Demis Hassabis
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For at least four decades the strongest computer chess programs have used alpha-beta search (18, 23). AlphaZero uses a markedly different approach that averages over the position evaluations within a subtree, rather than computing the minimax evaluation of that subtree. However, chess programs using traditional MCTS were much weaker than alpha-beta search programs, (4, 24); while alpha-beta programs based on neural networks have previously been unable to compete with faster, handcrafted evaluation functions.

AlphaZero evaluates positions using non-linear function approximation based on a deep neural network, rather than the linear function approximation used in typical chess programs. This provides a much more powerful representation, but may also introduce spurious approximation errors. MCTS averages over these approximation errors, which therefore tend to cancel out when evaluating a large subtree. In contrast, alpha-beta search computes an explicit minimax, which propagates the biggest approximation errors to the root of the subtree. Using MCTS may allow AlphaZero to effectively combine its neural network representations with a powerful, domain-independent search.
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https://arxiv.org/abs/1712.01815
https://arxiv.org/abs/1712.01815

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