Author: Peter McKenzie
Date: 11:02:27 01/26/99
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On January 26, 1999 at 11:56:50, Steve Maughan wrote: >I've heard of this technique but am not sure exactly what it is. Could someone >please explain it? Here is what I call razoring: Lets say we are doing a search to depth N, that means that at depth (N+1) we go into the quiescence search, meaning the side to move has the option of standing pat (setting alpha to the static score) or making a capture move. At depth N, if you have a really bad position and make a harmless move, the opponent will be able to make a cutoff at depth N+1 just by standing pat. With razoring, you try to avoid searching those 'harmless' moves. My implementation just goes straight to the quiescence search at depth N if the score is below alpha by at least 2 pawns. The reasoning being that a positional move that isn't a capture probably won't be able to raise the score by 2 pawns. For example, lets say we're searching the root position to depth 4, and we are searching the line 1.d4 e5 2.dxe5. At this point black is a pawn down and needs to do something pretty flash to prevent white from standing pat at the next depth and making a cutoff. At this point I would go straight to the quiescence search for black, where as without razoring you would search EVERY legal move. I've recently been experimenting with razoring, but haven't been happy with the results. A razoring version of lambChop beat a non-razoring version 26-24, which isn't statistically significant. The razoring version does alot worse on the ECM test suite getting 458/879 (20sec/move on P133) as opposed to 502/879 for the non-razoring version. A problem with razoring is that you will miss mates near the tips if your q-srch doesn't look at checks. Also, you have to be careful about interacting with lazy evaluation. Razoring will certainly reduce the number of nodes required to reach a given search depth, but I'm not convinced its a good tradeoff in my program. Regards, Peter > >Regards > >Steve Maughan
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