Author: Vincent Diepeveen
Date: 09:47:13 06/03/01
Go up one level in this thread
On June 02, 2001 at 22:00:22, Bruce Moreland 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 > >A recapture is supposed to be a relatively forced move. For example, in the >sequence PxP PxP PxP PxP, the second and fourth are recaptures, since that side >can't just go off and do something else without being down material. The first >and third are not recaptures -- they are optional. > >A reason you might want to experiment with these is that a capturing sequence is >relatively forced and easy to follow (especially for humans), yet consumes >plies. You don't want to run out of draft and miss a non-capturing stinger at >the end of the sequence. You also don't want to get hung up thinking you can >avoid something bad by using a recapturing sequence to induce the horizon >effect. > >I've heard people badmouth this extension, but I use it, because I think it >makes my own program tactically stronger, based upon tactical suite experiments. > You can easily do these experiments yourself, and either use the extension, >discard it, or fiddle with it until it works the way you want it to work. > >bruce If i use this then i search a full ply less in the complex middlegame. Usually i only do it when depthleft >= 4 ply or something similar. Of course i'm already doing loads of captures in the qsearch, which might explain why i need it less perhaps as others. In blitz it definitely improves strength because at 8 ply searches i don't feel recaptures that bigtime as at 10 or 11 ply (keep reducing 4 ply everywhere :)) At auto232 player the recapture extending version never scores better as one that doesn't have them. In general the only positive thing about recapture extension is that they solve loads of tactical position quicker for me.
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