Author: Severi Salminen
Date: 05:14:25 12/07/00
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>>You certainly need to clear the history table sometime. What happens when one >>entry overflows? If you don't ever clear your history table your move ordering >>is going to get really funky. >> >>History is a move ordering heuristic... because a move made 20 turns ago was >>good has nothing whatsoever to do with that move being good now. Keep the >>history table between iterative calls to search, sure... but don't keep it >>between moves, in my opinion. > >It is probably a bit better to decrease not clear the history table after a >move. History from 20 moves ago is certainly not worth much, but from 2 moves >ago ... yes. >Most increase counter by depth*depth btw. For me history doesn't help at all Thanks for both of you. Now it works smoothly. I must though experiment with many possibilities (how much to weight, when to weight (only if failhigh or even if score>alpha), how much to decrease after search...) >>A killer move is a great move at this ply. Like promoting a pawn or checking >>the king. THe idea is that you want to try this move again at the same depth in >>another branch of the tree earlier (and therefore cutoff earlier in the other >>branch). I do not make capture moves killers because, as Bob Hyatt said, >>captures are often not repeatable at different branches of the tree. I make any >>non-capture that results in a beta cutoff a killer move for its ply. I keep 2 >>killer moves and order these first before all other non-capture moves. I clear >>killer moves between top-level calls to Think (iterative search). >> > >Just one more note: if you use 2 killers and get a new one make the 2nd 1st and >replace the second one. Yep, so far I only use 1 killer. I think one could use counters. And replace the lower one maybe. But then again, is the one with most counts better that the recent one? Testing to do... I also think that one should not clear all killers after search, but to move them to previous ply level. What do you think? It sounds logical: if a move was great at ply 5 it should still be great at ply 4 after making a move? >>Your numbers for an 8 ply search of that position look sane. I had to check the difference between insane and sane in dictionary... :) Severi
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