Author: h.g.muller
Date: 02:58:04 02/15/06
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This is why I am experimenting with double accounting of ply depth, one counter for each side. Delaying tactics, like capturing the Rook, then only burn the ply budget of the side that initiates it if the recapture is a (singular) extension, and you will never be able to push anything over the horizon. But you have to be careful to also award extensions for solving threats like P attacks Q, or check evasion, which is much more difficult to control because threats can usually be solved in many more ways than recaptures. To recognize threats like forks or attack on trapped pieces at the horizon, you will have to judge quiescence from both sides, i.e. if you don't have any QS-allowed moves yourself, not automatically rely on static eval but throw in a null-move first to make sure there is no threat. And if there is a threat, award yourself the extension needed to neutralize it. (Which for forks of course is not possible, so you recognize the loss.) To prevent search explosion there should be strict limits on what the threat-evasion can do, it should not be used as an excuse to start a new offensive tactical combination on its own (that is a strict nono beyond the horizon, since it can be done from almost any quiet state). To achieve this, reduce beta to the current eval, just to prove that the node is not worse than that, i.e. the threat can be dealt with. (If your evaluation contains bonus points for having the move, you could negate these in a situation where there is a threat that you can solve, because apparently your move is already spoken for.) And of course you don't search just any move, but only the standard set of solutions to a threat (i.e. retreat, capture the attacker, block the attack, defend).
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