Author: Robert Hyatt
Date: 13:36:44 09/10/99
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On September 10, 1999 at 15:58:45, Ed Schröder wrote: > >For one moment forget about alpha and beta, you are on the wrong track as >alpha and beta are not a part at all of the code. You need an extra stack >that is set to -INF at each ply. Then before you do A/B you do the bestmove >calculation for that ply. Involved variables: SCORE and STACK, no alpha beta. > >Ed I understood that... but alpha and beta play a roll in this.. because each time you call Search() and then do your test with "best" when the score comes back, you get a bound... and nothing says that you get the _best_ bound on the score for each move you search, you only get a bound that is <= alpha. And they aren't directly comparable with each other, because the search stops as soon as any move at the next ply returns a score >= beta (which is <= alpha at the current ply). Even though there could be even _better_ moves were the search at the next ply to be completed. IE, we learn this: value for move1 <= 200 value for move2 <= 150 no way to say that the first is better than the second. We simply don't know that. It might be. Or it might not be, because the alpha/beta search done below this node doesn't supply that information. in any case, trying this was certainly slower for me, as the tree always got bigger, because I try the hash table move before _all_ other moves. And with this approach, for me, it was wrong far more than it was right, and the tree grew as a result.
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