Author: Robert Hyatt
Date: 22:09:31 07/23/99
Go up one level in this thread
On July 23, 1999 at 23:12:45, Scott Gasch wrote: >>actually you only can get a 'best' move from a "LOWER" bound (fail high) >>position. In an "UPPER" bound (fail low) all moves were bad and there is no >>'best' one. > >What is the best move in a fail high condition? Maybe I don't understand but it >seems like a fail high position is one where no successor move has beat alpha. >This is to say, alpha is the value of the best move in this position and none of >the successors beat it. Now that I have searched this node and determined it is >a fail high, how do I store the "best" move in the hash table when there is no >best move? > >It seems to me that only if the alpha < move < beta should I store a move in the >hash table...? A fail high move is a move where you call search recursively, and it returns a value == beta in this position. This means that the current move is "good" and no further searching is needed. The opposite case is you try the first move, search returns alpha, you try the second move, you get back alpha, you try the last move, you still get back alpha. None of the current moves are good enough to refute the move at the previous ply. You have no idea which one is the best move here either, you think they all are bad... you get a best move if value > alpha && value < beta as you suggest, also if value >= beta... So, simply stated, you get a best move if value > alpha... no matter what...
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