Author: Robert Hyatt
Date: 14:09:28 02/08/98
Go up one level in this thread
On February 08, 1998 at 14:10:44, Don Dailey wrote: >Hi Bob, > >>it was "debunked" because of hardware issues. Chess 4.6 searched 6 >>plies >>full-width on a cyber 176. Mac Hack could barely search 5 plies, with >>no >>q-search, using severely tapered forward pruning, because of hardware >>speeds >>in the 60's... IE Greenblatt couldn't even do a 2 ply search full-width >>at those speeds. >> >>What selectivity is all about is being careful at the root by going >>full- >>width, and taking risks farther out in the tree where you believe that >>even >>if you make a mistake, you have time to catch it in the full width part >>of >>the search next time and "fix" it. >> >>It's a trade-off... do you want to find deeper tactical things? Or do >>you >>want to find deeper positonal things? Selectivity overlooks things. No >>way to avoid it. Question is, does what it find offset what it >>overlooks? >>Good question. But your estimate of +100 is simply a wild guess. I'd >>suspect that a good brute-force program will play just as well as a good >>selective searcher. They will each find things the other overlooks. >>The >>selective searcher will find deeper things, the full-width searcher will >>find things the selective searcher pruned away in error. >> >>Take your pick. I tend to err on the side of simpler algorithms... >>fewer >>bugs means more wins... > > > >You need to expand on your statement that a good brute-force program >will play just as well as a good selective searcher. I don't agree >with this unless you are talking semantics (like calling Richard Langs >program full width because he does a few full width plys.) Marty's >program may be the closest thing among the really strong ones but I >think he just put's all the selectivity in the quies search. > >- Don Here's what I "think": A full-width search is going to hit N plies deep, using traditional ideas like iterative deepening, etc. A selective program is going to reach depth N+X, where X depends on how aggressively they prune in the forward direction. IE null-move is one way, static analysis is another, etc. When I talk about "selective" vs "brute-force" however, the idea is this: to selectively throw out moves (or selectively include them in the search) requires a finite amount of computation. To make this more accurate ramps this requirement up. What if it ramps it up enough that the very selective program does just as much work analyzing what to prune as the full-width program spends searching those moves that are no good? Something tells me that both converge to the same asymptotic bound at some point. IE I think it is just as hard to cull moves as it is to search them, if it is intended to beat world-champion class players. My old selective program looked like a genius in some positions, and like an idiot in others. Too many of the latter will kill overall performance, no matter how many times you look like a genius. It's far easier to lose based on one bad move than it is to win after playing 3 fischer-like moves... Selective programs run a risk of dumping a bad move here and there... whether the selectiveness comes from null-move (crafty) or something else (rebel, etc.)
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