Chinook is the first computer program to win the world champion title in a competition against humans. In 1990 it won the right to play in the human World Championship by being second to Marion Tinsley in the US Nationals. At first the American Checkers Federation and English Draughts Association were against the participation of a computer in a human championship. When Tinsley resigned his title in protest, the ACF and EDA created the new title Man vs. Machine World Championship, and competition proceeded. Tinsley won with four wins to Chinook's two, with 33 draws. In a rematch, Chinook was declared the Man-Machine World Champion in checkers in 1994 in a match against Marion Tinsley after six drawn games, and Tinsley's withdrawal due to pancreatic cancer. While Chinook became the world champion, it never defeated the best checkers player of all time, Tinsley, who was significantly superior to even his closest peer. In 1995, Chinook defended its man-machine title against Don Lafferty in a 32-game match. The final score was 1–0 with 31 draws for Chinook over Lafferty. After the match, Jonathan Schaeffer decided not to let Chinook compete any more, but instead try to solve checkers. At the time it was rated at 2814 Elo. The solution was achieved, and the result published in 2007.
Algorithm
Chinook's program algorithm includes an opening book, a library of opening moves from games played by grandmasters; a deep search algorithm; a good move evaluation function; and an end-game database for all positions with eight pieces or fewer. The linear handcrafted evaluation function considers several features of the game board, including piece count, kings count, trapped kings, turn, runaway checkers and other minor factors. All of Chinook's knowledge was programmed by its creators, rather than learned with artificial intelligence.
Timeline
1997 - Jonathan Schaeffer writes a book about Chinook called One Jump Ahead: Challenging Human Supremacy in Checkers. An updated version of the book was published November 2008.
May 24, 2003 - Chinook completes its 10 piece database with 5 pieces on each side.
August 2, 2004 - The Chinook team announces that the tournament opening in English draughts called the White Doctor is proven to be a draw.
January 18, 2006 - The Chinook team announces that the 09–13 21–17 05–09 opening is proven to be a draw.
April 18, 2006 - The Chinook team announces that the 09–13 22–17 13–22 opening is proven to be a draw.
March 10, 2007 - Jonathan Schaeffer announces that a final solution to checkers is expected within 3–5 months.
July 19, 2007 - The journal Science publishes Schaeffer's team's article "Checkers Is Solved", presenting their proof that the best a player playing against Chinook can achieve is a draw.
