Why is it so hard to write a good backgammon program?
There are two basic ways that a computer can play a game as well as or better than humans. One is to be really smart, the other is to do an awful lot of work. The general strategy most game-playing programs use is to use an evaluation function that isn’t very smart, but to make up for it by looking ahead a lot of moves (doing a lot of work). With chess, there are typically 20-30 moves by each player per turn. With backgammon, there are 21 unique rolls and often 4-6 ways to play each one (not counting doubles with could have 10 or more ways of playing). This makes it very difficult to look ahead very many levels. Looking ahead 3 moves by both players examining all possibilities when there are 25 choices at each play requires evaluating “only” 244 million positions. If there are 90 ways to play each move, there are 530,000 million, positions. With a game like chess, one can discard all but the best 5 or 10 plays per person. With backgammon, there are always 21 different choices of best p
