Author: Scott Gasch
Date: 20:23:53 08/15/01
Recently I've been messing around with singular extension (s.ex). As I see it, the problem with s.ex is that with alpha beta you do not have the precise value of a move -- you only have an upper or lower bound on the score. I am doing fail hard alpha beta and have been playing with this: If all moves in a position are terrible (less than alpha - delta1) except one... and that one is within delta2 of alpha, search that one move over again one ply deeper. I started doing this with delta1 = MATE-300 as I was hoping to find positions where there is only one move that will save you from mate. I've been gradually reducing delta1, though, and dumping the positions where it would extend. I also thought about changing the second condition: only extending if the one move was > alpha (that would have to mean it's a PV node because if it was a FH it would have returned immediately and never get to this code). What is the typical way to implement s.ex? What do you think about the ideas above? How do you do it? Thanks, Scott
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