Author: Peter McKenzie
Date: 14:29:38 03/07/99
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On March 07, 1999 at 16:34:47, Robert Hyatt wrote: <snip> >I have done this two ways: > >(1) first root move fails low, continue searching, hoping that another move >will not fail low and you get something useful. If you search all moves and >the score == alpha, you have to relax alpha and search again. > >(2) first root move fails low, relax alpha immediately and search it again to >get the true score for the first move. > >I do (2) at present, for a couple of reasons: (a) I want to know how far the >score dropped so I have some idea of how much trouble I am in and how much extra >time I might want to allocate; (b) It is not uncommon to 'win' a pawn in early >iterations only to see later that you can't hold on to it. So the old best >move is still best, but with a much lower score. It is more efficient to re- >search it immediately than to try all the other moves (which will also fail >low) and then try again. > >Which is better is a good question. I have seen cases where I wished I would >just continue searching, and others where I am glad I re-search after the first >move fails low. I do (1) in my program, I was thinking about this the other day and don't know which is best. Method (1) bets that if the first move fails low, there will usually be another move that doesn't fail low. Perhaps I'll add some stats to see if this is true or not. Perhaps an in between method is worthwhile: if the first move fails low, try another couple of moves with the existing alpha beta bounds. If they fail low, restart the search with the new apha beta bounds. cheers, Peter
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