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Along with [[Masaya Honjo]], [[Hiroyuki Iizuka]], and [[Masahito Yamamoto]], Kei Takada is author of the [[Hex]] playing program [https://www.game-ai-forum.org/icga-tournaments/program.php?id=755 Ezo], which played the [[17th Computer Olympiad|17th Computer Olympiad]] in [https://en.wikipedia.org/wiki/Yokohama Yokohama] 2013, and the [[18th Computer Olympiad]] in [[Leiden University|Leiden]] 2015. Ezo uses 2-ply [[Alpha-Beta|alpha-beta]] search with an [[Evaluation Functionfunction|evaluation function]] based on the theory of [https://en.wikipedia.org/wiki/Complex_network complex networks]. The function combines a betweenness measure of the player’s two sides with a shortest path metric that accounts for the degree of important nodes, further elaborted by Kei Takada at the [[Advances in Computer Games 14]] conference in Leiden 2015 <ref> [[Kei Takada]], [[Masaya Honjo]], [[Hiroyuki Iizuka]], [[Masahito Yamamoto]] ('''2015'''). ''[http://link.springer.com/chapter/10.1007%2F978-3-319-27992-3_21 Developing Computer Hex using Global and Local Evaluation based on Board Network Characteristics]''. [[Advances in Computer Games 14]], [https://acg2015.files.wordpress.com/2015/07/takada.pdf slides as pdf]</ref>. EZO switches to a [[Vadim Anshelevich#Hexy|Hexy-style]] evaluation when remaining time becomes short <ref>[[Ryan Hayward]], [[Broderick Arneson]], [[Shih-Chieh Huang]], [[Jakub Pawlewicz]] ('''2013'''). ''MOHEX Wins Hex Tournament''. [[ICGA Journal#36_3|ICGA Journal, Vol. 36, No. 3]], [https://webdocs.cs.ualberta.ca/~hayward/papers/rptYokohama.pdf pdf]</ref>. Ezo-CNN, which played the [[20th Computer Olympiad#Hex|20th Computer Olympiad 2017]], uses a [[Neural Networks#Convolutional|convolutional neural policy network]] for [[Move Ordering|move ordering]] <ref>[[Ryan Hayward]], [[Noah Weninger]] ('''2017'''). ''Hex 2017: MoHex wins the 11x11 and 13x13 tournaments''. [[ICGA Journal#39_34|ICGA Journal, Vol. 39, Nos. 3-4]]</ref> <ref> [[Kei Takada]], [[Hiroyuki Iizuka]], [[Masahito Yamamoto]] ('''2018'''). ''[https://link.springer.com/chapter/10.1007%2F978-3-319-75931-9_2 Computer Hex Algorithm Using a Move Evaluation Method Based on a Convolutional Neural Network]''. [https://link.springer.com/bookseries/7899 Communications in Computer and Information Science]</ref>.

* [[Kei Takada]], [[Masaya Honjo]], [[Hiroyuki Iizuka]], [[Masahito Yamamoto]] ('''2015'''). '': Developing Evaluation Function of Hex using Board Network Characteristics and SVM''. [https://www.jstage.jst.go.jp/browse/tjsai Transactions of the Japanese Society for Artificial Intelligence ], Vol. 30, No. 6]