Author: Peter McKenzie
Date: 17:43:22 01/22/00
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On January 22, 2000 at 17:40:10, Robert Hyatt wrote: >On January 22, 2000 at 03:12:53, David Blackman wrote: > >>On January 21, 2000 at 11:31:06, Robert Hyatt wrote: >> >>>The solution to the horizon effect is depth. And extensions. The most common >>>horizon effect type of move is a check, which constrains the opponent to react >>>to the check, and removes 2 plies from the depth. Extend on the check and you >>>cut the loss by 1 ply. A capture/recapture is the next most likely cause, as >>>a capture must either be followed by the recapture, a different capture to >>>maintain material balance, or a check. Again you lose 2 plies. And extending >>>on a capture/recapture pair will recover one of those plies. The capture, >>>check, get out of check, recapture group of moves is harder of course... >> >>Yes. You need extensions. Depth won't solve it on its own, but will make the >>program stronger. >> >>Recently i have tried a program that usually gets to 14 ply fairly quickly, but >>has almost no extensions. It plays reasonably well most of the time, but a >>couple of times i've seen it make obvious tactical errors. I mean obvious to me, >>without computer assistance, and i'm a 1500 player. >> >>Careful analysis of the positions showed it was the horizon effect. A simple >>tactic of 3 to 6 plies apparent depth was being missed because the computer >>could play a series of meaningless and perhaps slightly bad delaying moves to >>push the problem out past 14 plies so it couldn't see the main tactic. > > >reaching a depth of 14 plies should hide most horizon effect problems from any >but the very strong tactical players. But getting to 14 plies sounds impossible >for a primitive program, without some sort of selectiveness... and _that_ will >certainly cause tactical oversights... I think that 14 ply using nullmove pruning (R=2) and no extensions (not even check) and no fancy quiescence would still be prone to some quite bad tactical mistakes. Take the following classic type of position for example: [D]5k2/1p5r/3pp3/p2p4/1b1P1P2/qP1Q1NP1/P1P3N1/1K6 w - - Its obvious to a human that after Qxh7?? Bc3, white will be mated. The tricky thing for a program is to wade thru. the mindless checks by the white queen, and of course the null movers have a little trouble with the Qb2# threat. I think a vanilla 14ply null mover without any extensions would have a tough time avoiding Qxh7 though - even at depth 14.
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