Author: Christophe Theron
Date: 11:28:57 01/26/99
Go up one level in this thread
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
>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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