Author: Andrew Williams
Date: 13:55:53 04/28/99
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On April 27, 1999 at 15:35:06, Will Singleton wrote: >On April 27, 1999 at 12:28:41, Peter Kappler wrote: > >>r3r2k/p1bb1pp1/qp5p/3pP3/PBp2P1Q/4P1RP/2B3P1/R5K1 w - - bm Rxg7; >> >> >>P.S. Chess Genius 6 on my K6-300 finds Rxg7 instantly, and after a short time >>announces mate in 8. > > >Good position! We seem to have the usual discrepancy in number of moves to >mate: > >Chess Genius - Mate in 8 >Crafty - Mate in 9 >Hiarcs 6 - Mate in 10 (mate found in 10 seconds, likes Rxg7 right away) >MacChess - Mate in 8 (mate found in 12 minutes, likes Rxg7 after 2 min) > >Amateur doesn't find the move after 2 minutes and 9 ply, liking Be7 with +3. I >better get busy and try out the single-reply extension. Problem is, I use >psuedo-legal moves, so I'm not sure how to tell when I only have one reply! > >Will Hi Will, My program doesn't find this either. It likes Be7, but takes ages to see this. The reason I'm responding is that I've just implemented a single-response extension. I also generate pseudo-legal moves so I'm trying this: If I'm in check I extend one ply. I also check to see how many of the King's eight possible moves would be legal (I have a reasonably fast attacks_square() function for this). If this number <= 1, I then generate all the moves, make them and then see if I'm still in check. If only one of them gets me out of check, I extend another ply. Oddly enough, I seem to be able to do this pretty much "for free" (ie if I do all this and then don't extend it doesn't cost me much in the way of NPS). I've not tested this very thoroughly yet, but it seems to be OK. The nice thing is that I could extend fractionally when I find the King only has one safe square and then extend another fraction if it turns out he only way out of check. I haven't tried this yet. Having said all this, it doesn't help me with this particular problem. Hope this makes sense. Andrew
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