Author: Robert Hyatt
Date: 07:42:35 12/31/98
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On December 31, 1998 at 07:38:05, Inmann Werner wrote: >Hello > >Can anybody tell me how book learning works? >The principle should be, mark good moves as good and bad moves as bad. >But how can a program determine, what was a good or bad move? > >Werner There are two answers, and I use both in crafty: (1) if you lose a game, find the last book move where you had a choice of moves to make and mark the one you played as "never play again." This is the easy case and is called "result learning" in crafty. (2) take results from the first few searches after you leave book (I use 10 moves in Crafty) to get a feel for how the program likes the position. From these 10 search results, plus the rating of the opponent and the search depth of the moves, I compute a "learned value" that represents whether this position is good or bad, while factoring in the strength of the opponent and how long the search had, and then I apply this score along the book path working backward. At the first point where I had a choice, the move there gets the entire score added in. This score is then divided by the number of possible book choices at that position and this modified value is backed up further, getting divided every time there is more than one choice... Works pretty well, based on several hundred thousand games...
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