Author: Robert Hyatt
Date: 08:40:11 04/06/05
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On April 06, 2005 at 07:37:55, Johannes wrote: >Hello! >Right now im working on a new Version of my Chess Engine and an idea has come to >my mind, but i dont know if its applicable: >When I'm in Q-Search i only want to deal with material values. I handle theses >incrementally, so theres is no need for any function call except the Q-search >recursion. >After returning from Q-Search (at the full-width horizon) i simply add the >positional eval score to the score returned from Q-search. This score is >returned "up the tree". >For the positions before the horizon this should be no problem concerning >alpha/beta values etc... . Also positions beyond the horizon should not suffer >from this, as long as the alpha/beta values were not passed to a Node before the >horizon before. If they were, the alpha/beta bounds would not be correct, >because they include positional scores which are not considered beyond the >horizon. >So my idea is to simply substract the local positional score from the alpha/beta >values (as long as they are not -INF or +INF) at the full-width horizon, before >entering Q-Search. I assume that this would result in correct cutoffs. >Is this idea correct? >I didnt find any drawbacks yet, but i only have a vague intuition about it. >I really would appreciate if anybody could help me with this. >greets >johannes You can "cheat the system" however you want. In this case, you are positionally evaluating the board, and then making captures that could greatly change that positional evaluation, but you won't realize it. For example, a capture that shreds the king-side pawn structure will not be scored correctly since you won't realize that the king-side is destroyed, because you use the positional evaluation before the capture is made and just factor in material only after that point. Ditto for endgame ideas such as a pawn running after all pieces are exchanged. If you evaluate the position before the exchanges, the pawn can't run, if you then make the exchanges and think all is ok, you will lose. It is a dangerous road...
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