Author: Miguel A. Ballicora
Date: 09:36:42 01/09/02
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On January 09, 2002 at 11:30:34, Ulrich Tuerke wrote: >On January 09, 2002 at 10:15:53, David Rasmussen wrote: > >>Some time ago we talked about the recapture extension. Bob's experiments with >>Crafty seemed to show that recapture extension was a bad idea at least for his >>program. > >I don't know if the notion "the recapture extension" is really so well defined. >I think that there are several ways to support recapture extensions; I don't >know what Crafty does. > >A long time ago, I have experimented a lot with these extensions. >Currently (IIRC), I extend when there is a capture and in the subsequent half >move there is another capture to the same square gaining the same material >(ignoring the difference between bishop and knight). I do this extension at most >once in a line. I restrict it a bit more. It has to be not only a recapture on the same square, with the same material but also has to be the ONLY recapture possible in that square. In other words, after e4 e5/Nf3 Nc6/Bb5 a6/Bxc6 I do not extend because there is two possible recaptures. After e4 e5/Nf3 Nc6/Bb5 b6/Bxc6 I extend because there is only one possible recapture. In this way it is very difficult that the tree will explode, IMHO. Of course, the usefulness is limited too. Regards, Miguel > >This isn't too expensive and helps a bit in tactics. > >I have also tried to make this extension independent on the square (i.e. just >re-gaining the same material one ply later), but I wasn't completely happy with >it. > >Another idea is to define a recapture as 2 subsequent captures to the same >square bringing the score back into the aspiration window. I'm afraid that this >may be expensive at the start of an iteration where alpha-beta usually uses a >larger window. It could also produce some search anomalies because I'm not sure >if in all cases the condition for extension will be reproduced in the >verification search. > >Anyway, this extension generates some path dependence, i.e. may occasionally be >missed by transposition table entries. > >Just some simple ideas ... > >Uli > >> >>How many people have the recapture extension because they positively believe >>that it is better for their program, and how many has removed it from their >>program because the positively believe that it is bad for their program? >> >>I am sure a lot of people have it or don't have it, but for no specific reason, >>that is, they have not tested the effect of this extension thoroughly. >> >>/David
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