Author: Eugene Nalimov
Date: 11:47:35 01/26/99
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On January 26, 1999 at 14:28:57, Christophe Theron wrote: >On January 26, 1999 at 14:02:27, Peter McKenzie wrote: > >>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. > > >What you are describing is called "futility pruning". Razoring is something >different, much more risky. > > > Christophe I beleive that "futility pruning" is just a special case of "razoring". I used to think that "razoring" is forward pruning where you decide to ignore some moves based on static evaluation of the position (as opposed to null move, where you first search with a lesser depth, and other similar ideas). If I'm correct, than "futility pruning" is just a "razoring" when depth=1. And it's much safer than other variants of "razoring", or at least safer when you cannot spend thousands lines of code for more detailed position analysis before performing "razoring". Eugene > > >>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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