Author: Robert Hyatt
Date: 07:04:13 02/03/99
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On February 02, 1999 at 23:32:56, Melvin S. Schwartz wrote: >You stated that Selective Search looks deeper but with intrinsic error. Then you >said Brute Force takes longer but will get to the same depth without the errors. >Now, how could you say Selective Search looks deeper and then say Brute Force >takes longer but gets to the same depth? take a game where each side has exactly 10 moves at each 'node' in the tree. If the 'brute force' program searches to depth=5, it will search 10^5, or 100,000 nodes. If that is a limiting factor (it usually is, in that most programs search a reasonably similar number of nodes per second if they are pretty equal in skill) then you are stuck with 5 plies until you can search faster. The selective program might choose to only search 5 of the 10 branches from each node (hence it 'selects' which 5 to follow, commonly called 'forward pruning'). And as a result, it can search to depth = log5(100000). If you figure that out, you get roughly 7 plies of search (5^7 is close to 100000). Now if your 'selectivity' is good, you search two plies deeper than I do, and you will find tactical things I don't and win. If your selectivity is bad, you will search 2 plies deeper than I do, but overlook something here and there that causes you to lose instead. That's how it _can_ play better, because it can go deeper. But that's how it _can_ play worse, because it overlooks things that the brute-force program won't. >Also, are you saying that one method results in a higher chess rating? If so, >which do you feel would have a higher chess rating? >The SSDF (Swedish Rating System) always rates the chess computers with Selective >Search. From my limited experience playing against both methods, I find that >Selectve Search does on some occasions make a better move than Brute Force. So >far I have not found the reverse to be as common. Although I must admit the >occasions where there is a difference in the move seems to be rather infrequent. it happens. Wchess is selective in some way. And I have sent Dave several positions in the past where it just 'fell apart' unnecessarily. (We play a lot on ICC). He fixes those and gets better. Nowadays he makes few tactical mistakes, but sees more with his selective search and is _very_ strong as a result. >It appears from the limited response to this controversy that it has not really >stirred up much of an interest from other club members. >Mel it's old news and old discussion. This has been discussed since the 1950's in fact. :)
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