Author: Ulrich Tuerke
Date: 09:53:58 01/09/02
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On January 09, 2002 at 12:36:28, Miguel A. Ballicora wrote: >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. Sounds to me like a very reasonable idea. Uli > >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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