Author: William Bryant
Date: 19:14:10 05/28/99
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On May 28, 1999 at 09:38:24, Robert Hyatt wrote: >Here is the problem in your case. Fine 70 takes 26 plies to solve, and there >is _no_ way to see winning the pawn any quicker. So how does crafty find it >at depth=18? Poor move ordering somewhere. What happens is it finds a way to >win the pawn with black playing poorly, then discovers that it can force a >position to be reached with black playing perfectly, where this position was >already reached with black playing poorly and it found that below this position >even if black plays perfectly it can force a win. This will be 100% repeatable >with a serial search. But with the parallel search, not at all. And you get >such wild results. Normal positions don't behave like this, but fine 70 is >solved by 'cheating' (a program with perfect move ordering will take 26 plies >no matter what). And this 'cheating' is screwed up by a non-deterministic >parallel search. Thank you for this explination. An early version of my program seemed to find this quickly - ply 13 or 14 but as I improved the search, added hash tables, etc. it was unable to find it. One of the things I did was try to improve move ordering when I added PVS. Based on this explination, I reran the position at much longer time controls. And as expected, after completing the pv search at ply 26, it found Kb1. I was worried I had introducted even more bugs. William wbryant@ix.netcom.com New Board Position 8/k7/3p4/p2P1p2/P2P1P2/8/8/K7 w - - bm Kb1; Move 1 W>> PLY NODES TIME SCORE PV ____________________________________________ 5 275 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 6 543 0:00 +1.10 Kb2 Kb6 Kc3 Kc7 Kc4 Kd7 7 1109 0:00 +1.10 Kb2 Kb6 Kc3 Kc7 Kc4 Kd7 Kd3 8 1486 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 9 1994 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 10 3150 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 11 4270 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 12 6245 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 13 8655 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 14 13901 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 15 21739 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 16 40467 0:00 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 17 70422 0:01 +1.20 Kb2 Kb6 Kc3 Kc7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 18 152929 0:02 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 19 157027 0:02 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 20 782424 0:09 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 Kd3 21 1061001 0:12 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 Kd3 22 1516019 0:17 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 Kd3 23 2294026 0:26 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 Kd3 24 4604394 0:52 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 Kd3 25 8159291 1:33 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 Kd3 26 19884533 3:48 +1.20 Kb2 Ka8 Kb3 Ka7 Kc4 Kb6 Kd3 Kc7 Kc4 Kb6 Kd3 26 35671585 6:46 +1.60 Kb1
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