Author: Inmann Werner
Date: 03:00:43 06/02/98
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> >Hi Innman, > >I did not look at the position yet, but I know that Alpha/beta will >not throw out a good move. One well known characteristic of alpha/beta >is the fact that it will ALWAYS give you the same result as a >full width search with no alpha beta. This is fact, so perhaps >there is simply a bug. > >If the queening move occurs in the quies search, and you have a >typical quies search where each side has the option to play a >null move and stop, then the opponent will take this option >rather than allow the program to queen. > >Look for these things. Another thing to try is a simple >technique of moving forward. Play the correct first move and >see how many it takes. Keep walking forward until it should >see it with a 1 ply search and note its behavior. This might >give you clues to find the bug, or understand what is going on. > >- Don Hi Don! Yes. Alpha beta does not throw away good moves. But it throws away bad moves. Example: Its black to move and we are in the quiet search of alpha beta. (Only beating moves and so). If black beats the white pawn, white has a running pawn. For black, the rating is much lower then alpha and lower than beta. So, it is not counting! As I said, also Fritz did not get it until depth 9. Small source from alpha beta if (eval>=beta) new_bestmove (Cutoff) if (eval>alpha) new_bestmove (better alpha) else ?? Werner
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