Author: Robert Hyatt
Date: 11:44:58 06/03/99
Go up one level in this thread
On June 03, 1999 at 14:40:44, Eugene Nalimov wrote: >The good strategy is to maintain 2 killers, and when the move causes the cutoff, >check: if it is killer#1, do nothing; if it is killer#2, swap killers; if it is >new one, move killer#1 to killer#2, and that new move to killer#1. Also, if the >move is capture of the opponent's piece that just was moved, do not store it as >killer, as it's likely that move will not be good in the next position (that >means that you have to try those captures first, before considering killers - >very reasonable, as in the half of nodes we have to try every move, and after >majority of moves you can easily win the material by just capturing moved >piece). > >Eugene I don't even store captures as killers, since good captures are tried before the killers anyway... > >On June 03, 1999 at 14:29:23, Andrew Williams wrote: > >>On June 03, 1999 at 12:59:02, William Bryant wrote: >> >>>Every time I try to improve my program, I seem to break it in innumerable ways. >>> >> >>Join the club :-) >> >>>The killer move heuristic should be rather easy to implement. >>> >>>At every ply, any move that generates a cutoff (I interpret as a beta cutoff, a >>>fail high), this move is added to the current killer table. >>> >> >>This is what I do. >> >>>Is it an alpha cutoff (score > alpha) more appropriate? >>> >>>Also, does this move automatically displace previous killer moves, or do you use >>>some qualifier such as the search score, keeping the moves with the greates >>>score? >> >>What I use is a count for how many times the killer move has been successful >>(caused a cutoff). The least successful gets replaced. >> >>> >>>Finally, in using the killer moves for move ordering the ranking I am using is: >>>1. Hash Table Move >>>2. PV Move (in not the same as #1) >>>3. Captures with a net positive score (captured piece > capturing piece) >>> Promotions >>>4. Killer moves and Captures with an equal score (exchange) >>>5. Loosing Captures >>>6. All other moves--sorted by the history heuristic. >>> >>>Any help will be appreciated, I am missing something simple because this is >>>slowing down, not speeding up my search. >>> >> >>How many killers are you using? (I find that changing the number of killers >>makes quite a difference). Are you checking killers before generating your >>moves? This (I think) was the original justification for killer moves; you can >>try them before even generating moves at the current ply. If you do this, you >>must be careful to ensure that the killer is valid in the current context, as it >>may have arisen from a quite different position. >> >>I hope others will also answer this question, as I have never found killers >>to be a particularly big win either. Normally I just use the history heuristic. >>At the moment, I'm keeping a couple of killer moves and checking for them >>when I generate moves. This isn't in the "spirit" of the killer heuristic, but >>it seems marginally better. >> >> >>Andrew Williams
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