Author: Christopher R. Dorr
Date: 08:40:58 01/25/99
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On January 24, 1999 at 18:47:33, Melvin S. Schwartz wrote: >I read your review of the Novag Diamond 11 where you stated that Selectivity On >increases the playing strength. I contacted a technical advisor at Saitek in >Hong Kong who assured me that Brute Force examines the position more extensively >and minimizes the risk of an occasional oversight. This would indicate beyond >any doubt that Selectiviy Off and Brute Force On would result in better chess >play and a higher rating. Since the Novag Diamond, according to ICD's >literature, has Selectivity and Brute Force, your article would seem to be >inaccurate when you state that the Novag Diamond, and other chess computers with >Selectivity "On" would result in a higher rating. Even in the manual I have with >my Mephisto atlanta - a chess computer you have as yet failed to review - it >states that Selectivity will compute faster but Brute Force is a powerful >program which will minimze the risk of an occasional oversight. That could only >mean that Brute Force searches more extensively to reduce the possibility of an >error. With more time for searching, I have to believe that Brute Force, not >Selectivity, would result in a higher rating. >Please investigate this matter further and let me know your results. >Best regards, >Melvin S. Schwartz >e-mail: pipesmoker-1@webtv.net Unless this 'selective search' is different from conventional definitions of 'selective search', selective search is *most definitely* stronger than brute force. regardless of what the tech guy said. The reason is as follows (somewhat simplified). Brute force eveluates *every position* is every branch of the search tree to a certain depth, dictated by time constraints. Lets say that (in time control x) that the brute force mode is able to examine every single position arising from the current position up to depth 8 ply. That mean that the computer sees *every* possible position that can arise in the next 4 full moves, and make is decision based on what it can force within that search depth. The selective search mode utilizes it's time differently. It may well search the first (say) 4 or 5 or 6 plies completely (ala brute force), but it will selectively search out in certain lines much deeper (say to 10 or 12 or 14 ply). If the position is tactically intersting (and therefore extended), this mode may well find a win of a pawn on ply 6/14 (i.e. 6 ply brute force, extended to 14 ply in certain lines). There are, of course, trade offs with each method. The selective search may miss a tactic in a line that it prunes off at ply 5 at ply 8 in that line that brute force sees. This isn't terribly likely, as selective search will follow a given line down further as long as it's tactically 'interesting'. Brute force's trade off comes because it sees *nothing* beyond a certain depth, because it has to spend it's time examing every position in it's given search depth, regardless of how ridiculous or unpromising it might be. The trade offs with brute force generally cost a program *far more* rating points than do the trade offs of selective search. I've owned dozens of programs and dedicated chess computers, and cannot remember any of them playing as well with brute force search as with selective search. Chris
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