Author: Andrew Platt
Date: 04:08:48 09/03/04
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On September 03, 2004 at 00:43:27, Stuart Cracraft wrote: >So today I find out that my recapture is bad. It must be. Bob said so. > >I take 1 minute to reimplement it to be "extend on 2nd capture on the same >square in a row" because I heard someone else talking about that's the >way they do it and got a surprise a minute after that. > >The result is that Qxf4 for Win-at-Chess comes into view >in 98 seconds and holds after having been missed after seemingly >endless runtime with the old bad recapture in or out. Of course >it is nothing like the 13,000 nodes that Tord (was it?) solves >141 in. Perhaps we should have a contest for who solves 141 in >the fewest moves. He would surely win. It takes me 24 million. >I admire a search that is so directed in so few nodes. Surely >we pay homage to Berliner with it, eh? Retire in peace in Florida >and then two category 4 storms hit. Unlucky fellow. Congrats but I seriously think there must be something strange if mate threat extensions don't help. I don't have recapture extensions (yet) but the mate threat brought it down from a 13 ply search to an 11 ply one. It's still way too expensive because the tree is very large at that point and with the alpha-beta window being wide open for the mate score it takes forever. Right now I'm focussing on why it doesn't get it sooner; after that I'll implement re-capture extensions. I think that looking at checks in the quiescent search would have helped me a little. When analyzing the trace files I see the null move dropping straight into quiescent search with a mate (e.g. a null move after Qxf4 Bxf4 Rxh5 - null - Rh8#). However, all it does is the stand pat evaluation which causes a beta cutoff. It would be too expensive for me to really deal with checks in qsearch because I don't want to have to generate the legal capture modes. All I do is bomb out of it if I see the King being captured. However, it might not be too expensive to generate the legal moves at the first ply of qsearch if we're in check to catch these conditions. I might try that and see if it causes testsuites to slow down much. Andy.
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