Author: Vincent Diepeveen
Date: 09:50:04 06/02/01
Go up one level in this thread
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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