Computer bridge

Computer bridge is the playing of the game contract bridge utilizing computer software. Following years of limited progress, at the end of the twentieth century the field of computer bridge has made major advances. In 1996 the American Contract Bridge League (ACBL) established an official World Computer-Bridge Championship, to be held annually along with a major bridge event. The first championship took place in 1997 at the North American Bridge Championships in Albuquerque. Since 1999 the event has been conducted as a joint activity of the American Contract Bridge League and the World Bridge Federation.

World Computer-Bridge Championship

The World Computer-Bridge Championship is typically played as a round robin followed by a knock-out between the top four contestants.^[1] Winners of the annual event are:

• 1997 Bridge Baron
• 1998 GIB
• 1999 GIB
• 2000 Meadowlark Bridge
• 2001 Jack
• 2002 Jack
• 2003 Jack
• 2004 Jack
• 2005 Wbridge5
• 2006 Jack
• 2007 Wbridge5
• 2008 Wbridge5
• 2009 Jack
• 2010 Jack
• 2011 Shark Bridge

Computers versus humans

In Zia Mahmood's book, Bridge, My Way (1992), Zia offered a £1M bet that no four-person team of his choosing would be beaten by a computer. A few years later the bridge program GIB, brainchild of American computer scientist Matthew Ginsberg,^[2] proved capable of expert declarer plays like winkle squeezes in play tests. In 1996, Zia withdrew his bet.^[3] Two years later, GIB became the world champion in computer bridge, and also defeated the vast majority of the world's top bridge players from the 1998 Par Contest (including Zia Mahmood). However, such a par contest measures technical bridge analysis skills only, and in 1999 Zia beat various computer programs, including GIB, in an individual round robin match.^[4]

Further progress in the field of computer bridge has resulted in stronger bridge playing programs, including Jack ^[5] and Wbridge5.^[6] These programs have been ranked highly in national bridge rankings. A series of articles published in 2005 and 2006 in the Dutch bridge magazine IMP describes matches between five-time computer bridge world champion Jack and seven top Dutch pairs including a Bermuda Bowl winner and two reigning European champions. A total of 196 boards were played. Jack defeated three out of the seven pairs (including the European champions). Overall, the program lost by a small margin (359 versus 385 imps).

Cardplay algorithms

Bridge poses challenges to its players that are different from board games such as chess and go. Most notably, bridge is a probabilistic game: a bridge player must decide which bid to make and which card to play based on only incomplete information. At the start of a deal, the information available to each player is limited to just his/her own cards. During the bidding and the subsequent play, more information becomes available via the bidding of the other three players at the table, the cards of the partner of the declarer (the dummy) being put open on the table, and the cards played at each trick. However, it is only at the end of the deal that full information is obtained.

Today's top-level bridge programs deal with this probabilistic nature by generating many samples representing the unknown hands. Each sample is generated at random, but constrained to be compatible with all information available so far from the bidding and the play. Next, the result of different lines of play are tested against optimal defense for each sample. This testing is done utilizing a so-called double-dummy solver that via extensive search algorithms determines the optimum line of play for both parties. The line of play that generates the best score averaged over all samples is selected as the optimal play.

Efficient double-dummy solvers are key to successful bridge-playing programs. Also, as the amount of computation increases with sample size, techniques such as importance sampling are used to generate sets of samples that are of minimum size but still representative.

The future

In comparison to computer chess, computer bridge is in its infancy. Yet, whereas computer chess has taught programmers little about building machines that offer human-like intelligence, more intuitive and probabilistic games such as bridge might provide a better testing ground.

The question whether bridge-playing programs will reach world-class level in the foreseeable future is not easy to answer. Computer bridge has not attracted an amount of interest anywhere near to that of computer chess. On the other hand, researchers working in the field have accomplished most of the current progress in the last decade.

Irrespective of the results of computers against humans in tournament bridge, computer bridge already has changed the analysis of the game. Commercially available double-dummy programs can solve bridge problems in which all four hands are known, typically within a second. These days, few editors of bridge books and magazines will solely rely on humans to analyse bridge problems before publications. Also, more and more bridge players and coaches utilize computer analysis in the post-mortem of a match.

References

1. ^ ACBL/WBF World Computer-Bridge Championship Official Site
2. ^ GIB
3. ^ Zia's bet and the rise of computerbridge as reported in the Netherlands bridge magazine IMP
4. ^ Foreword to Man vs Machine - The Bridge Match of the Millennium
5. ^ Jack homepage
6. ^ WBridge5 homepage (in French)

External links

• Matthew L. Ginsberg, GIB: Steps Toward an Expert-Level Bridge-Playing Program
• Paul M Bethe, The State of Automated Bridge Play, January 14, 2010