Author: Robert Hyatt
Date: 13:10:11 12/14/98
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On December 14, 1998 at 05:34:41, Andrew Williams wrote: >Hello all, > >I'm trying to work out how to implement capture/recapture extensions in >my program. I have had a look at crafty and gnuchess and I've tried >several approaches, viz: > >1 Extend when a capture followed by recapture restores the material > balance we had at the root. Suggested by Berliner (HiTech). I don't do this any longer. It was overly restrictive (IMHO). But always worth trying again. > >2 Extend when the capture/recapture restores the material balance from > before the sequence. Another variant... basically you are looking at two equal captures on successive plies. I don't do this either. This is more liberal than option three below, because now you can reach positions where the queens "run amok". IE Qxh7 Qxa2 is a recapture, then Qxh8 Qxa1 is a recapture, and the queens merrily eat everything in sight, all the while extending every other ply. I don't do this... > >3 Extend when the capture and recapture are on the same square (and same > material value). > This is my simple approach that seems to work ok. You can try the idea that Ken Thompson proposed in 1983, that of counting normal moves as 1 ply, but only counting captures as 1/2 ply. He decided (after the 1983 WCCC tournament) that this wasn't a good way to do it as, in his words, "it costs 1/2 ply to do this..." >In all these cases, I seem to get a much larger tree and often lose a ply >of search because of this. So, three questions: > >(a) Am I on the right lines with 1, 2 and 3 above? >(b) Is it normal to lose depth when doing this? The total nodes you can search is fixed by your search speed and the time per move you are alotted. So if you increase the depth on some moves, you have to reduce it on others... no other way to make things work. This is perfectly normal and is "the tradeoff" we often mention here... >(c) Generally speaking, it better to complete d7 with this extension than > d8 without it? > Would you rather have 7 apples or 8 oranges? IE it is not an easy question to answer. Those that do this extension believe it works. Those that don't, don't. It can help, in the right places, while it can hurt in others... >I realize that these questions probably aren't yes/no style questions, so >thanks to anyone who takes the trouble to reply. > >Regards > >Andrew Williams >(Author of PostModernist on ICC)
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