Author: Robert Hyatt
Date: 14:40:10 01/22/00
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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...
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