Author: Vincent Diepeveen
Date: 09:50:04 06/02/01
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On June 02, 2001 at 05:17:33, Georg v. Zimmermann wrote: >On June 01, 2001 at 16:13:41, Scott Gasch wrote: > >>Hi all, >> >>I have some questions about recapture extensions. >> >>First of all, what is the point? I assume to extend in a position where a >>recapture move is the only reasonable move so as to see further beyond the >>forced exchange. Somewhat like singular extensions or one legal reply >>extensions, I think a properly done recapture extension should not be too >>expensive. I'd also expect that a well done recapture extension would improve >>the tactical strength of the engine. >> >>Well, I've been trying to get a good recapture extension working on my engine >>for a while now. I've tried a bunch of different recapture definitions / >>conditions. Most recently I did: >> >> 1. last move was a capture and this move captures the last moved piece >> 2. this is the first capture considered (weighed by SEE) >> 3. do not allow two recaptures in a row >> 4. this move restores the material balance to what it was at the root. >> >>...in which case I extended 1/2 ply. Since I am expecting better tactical >>ability with the recapture turned on, I test it with the ECM suite. Every time >>I try, my results are worse with the recapture turned on than with no recapture. >> >>I know that a bunch of other engines are doing recapture... so there must be a >>good idea there somewhere. Can anyone address these questions or propose a >>solid recapture condition? >> >>Thanks, >>Scott > >I do this : > > /* Capture extensions. */ > > if ( CapturedPiece[ply-1] && > (ply > 1) && > (treemoves[ply-2].to() == treemoves[ply-1].to()) && > (!AIBoard.getattacks(AIBoard.getColorOffMove(), > (treemoves[ply-1].to()) ) ) ) > > { > extensions += CAPTURE_EXTENSION; > /* [... some debug stuff ] */ > } > >In other words : > >If I capture to the same square and no other capture to that square was >possible, extend by half a ply. > >This helps a lot in my program, for Crafty the last time I tried it solved one >WAC position more. So you sacrafice your soul to solve one WAC more at 1 second a position? >Regards, >Georg v. Zimmermann
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