GIB: Steps Toward an Expert-Level Bridge-Playing Program

This paper describes GIB, the first bridge-playing program to approach the level of a human expert. (GIB finished twelfth in a hand-picked field of thirty-four experts at an invita-tional event at the 1998 World Bridge Championships .) We give a basic overview of the algorithms used, describe their strengths and weaknesses, and present the results of experiments comparing GIB to both human opponents and other programs. 1 Introduction Of all the classic games of mental skill, only card games and Go have yet to see the appearance of serious computer challengers. In Go, this appears to be because the game is fundamentally one of pattern recognition as opposed to search; the brute-force techniques that have been so successful in the development of chess-playing programs have failed almost utterly to deal with Go's huge branching factor. Indeed, the arguably strongest Go program in the world (Handtalk) was beaten by 1-dan Janice Kim (winner of the 1984 Fuji Women's Championship) in the 1997 Hall of Champions after Kim had given the program a monumental 25 stone handicap. Card games appear to be different. Perhaps because they are games of imperfect information, or perhaps for other reasons, existing poker and bridge programs are extremely weak. World poker champion Howard Lederer (Texas Hold'em, 1996) has said that he would expect to beat any existing poker program after five minutes 1 play.* 1 Perennial world bridge champion Bob Hamman, six-time winner of the Bermuda Bowl, once summarized all of the commercial bridge programs by saying that, "They would have to improve to be hopeless."+ In poker, there is reason for optimism: the GALA system [Koller and Pfeffer, 1995], if applicable, promises to produce a computer player of unprecedented strength by 1Many of the citations here are the results of personal communications. Such communications are indicated simply by the presence of a + in the accompanying text. reducing the poker "problem" to a large linear optimization problem which is then solved to generate a strategy that is nearly optimal in a game theoretic sense. Scha-effer, author of the world champion checkers program CHINOOK [Schaeffer, 1997], is also reporting significant success in this domain [Billings et al., 1998]. The situation in bridge has been bleaker. In addition, because the American Contract Bridge League (ACBL) does not rank the bulk of its players in meaningful ways, it is difficult to compare the strengths of competing programs or players. …