Author: David Blackman
Date: 00:12:53 01/22/00
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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.
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