Author: Robert Hyatt
Date: 07:45:20 01/11/98
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On January 11, 1998 at 08:51:06, Carsten Kossendey wrote: >On January 11, 1998 at 01:07:46, Stuart Cracraft wrote: > >>Someone on this newsgroup wrote about a useful extension >>that went something like "If the null move search returns >>a mate score, e.g. n moves to mate, then extend." > >If you use recursive null moves, you will want to limit it to small N's >since otherwise you start extending lines where your opponent moves 6 >times in a row or something, and even the most quiet positions look like >mates then ;) > I do recursive null-move, but *never* two null-moves back to back, so that this isn't a problem. For me, turning this on (plus the hashing enhancement I described after Bruce explained his basic idea) means Crafty now finds Win At Chess 141 in under 30 seconds. This position has eluded solution (by Crafty) for a couple of years. In one minute per move, I now only miss 2 on a P6/200... number 160 and number 230. 160 still takes 4 minutes or so, while 230 I don't know. The good news (for me) is that Crafty is now approaching Cray Blitz in tactical skill *if* hardware is equal. Cray Blitz still solves 297 in less than 1 second, and gets all 300 in 1 second or less (it only times to the nearest second, so a 1 second limit really means up to 1.5 seconds per position or so. Crafty can do all but 2 in 60 secs at 100K nodes per second. Based on Cray Blitz's speed of 5M nodes per second on a 2ns T90, Crafty should be able to hit around 10M nodes per second, or be about 100X faster than it is now. That would put it solving all but 2 in under 1 second. null-move R=2 seems to affect 230, because the first move tosses a rook, and null-move searches below that tend to fail high... >>I didn't see any improvement (with limited testing) after >>implementing this. Is it basically in time-to-solve or >>seeing more solutions? >> >>Where's the beef? >> >>--Stuart
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