Author: Slater Wold
Date: 22:19:37 10/20/01
Go up one level in this thread
On October 20, 2001 at 15:09:16, Jeremiah Penery wrote: >On October 20, 2001 at 08:57:03, Slater Wold wrote: > >>On October 20, 2001 at 05:10:13, Simon Finn wrote: >> >>>On October 18, 2001 at 23:34:45, Slater Wold wrote: >>> >>>>On October 18, 2001 at 22:55:02, Dann Corbit wrote: >>>> >>>>>On October 18, 2001 at 21:01:46, Slater Wold wrote: >>>>> >>>>>>On October 18, 2001 at 09:14:43, José Antônio Fabiano Mendes wrote: >>>>>> >>>>>>> L.D.Evans-Haik,London 1978 [unusual and difficult position] >>>>>>> [D]8/p2P3P/k7/8/8/2q5/6PK/1Q6 b >>>>>>> "Surprisingly Black can deliver perpetual check or force stalemate." >>> > ><SNIP> >>>>>> Qa2+ 13. Kd6 Qd2+ 14. Kc7 Qc2+ <HT> >>>>>> 16 46.88 -- 1. ... Qe5+ >>>>>> time=60:01 cpu=201% mat=2 n=1693306751 fh=99% nps=470k >>>>>> ext-> chk=1363197943 cap=274706 pp=267447 1rep=117221890 mate=2380 >>>>>> >>>>>> predicted=0 nodes=1693306751 evals=7323296 >>>>>> endgame tablebase-> probes done=48149 successful=4738 >>>>>> hashing-> trans/ref=73% pawn=99% used=14% >>>>>> SMP-> split=4869 stop=472 data=13/32 cpu=120:40 elap=60:01 >>>>>>Black(1): >>>>>> >>>>>> >>>>>>Fails low @ 46 seconds, and can't resolve it in 59 minutes. :( >>>>> >>>>>This looks like a bug. That position should never fail low, but always fail >>>>>high. >>> >>>Why? The position is ultimately drawn, but that doesn't mean there won't be some >>>nasty shocks on the way. >>> >>>>> >>>>>Either that, or crafty may have found some strange, suicidal attack that >>>>>succeeds. >>>> >>>>If I had to guess, I'd say it'll find something. I did it with 10 minutes at >>>>first, and it did this same thing. 59 minutes to resolve a fail low _does_ seem >>>>a tad long. Perhaps Bob can help here. >>> >>>I had a long look at this position yesterday. >>> >>>White will win if he can get his king to a1 - this allows him to >>>interpose the queen and eventually kill the checks. >>> >>>To prevent this, Black has to answer Ka2 with Qa4+/Qa5+ and Kb2 with Qd4+/e5+. >>> >>>This requirement restricts where Black can check when the White king is on other >>>squares too. >>> >>>I think (but I'm not 100% sure) that answering Ke3 with Qg3+ loses >>>because the White king can eventually get to a1. >>> >>>Crafty may just have discovered this and needs to spend a >>>lot of time finding an alternative system of defence that works. >>>(Black should arrange things to answer Ke3 with Qc5+, for example.) >>> >>>Simon >>> >>>> >>>>I can give it more time, if requested. >> >>That's a very good explaination. However, after about 54 billion nodes, I would >>expect it to have exhausted all of these possibilities. :) > >I think Crafty has some search flaws that cause this kind of behavior. I've >seen cases like this (I'm just making up these moves because I don't have an >actual position handy): > >1) The move Ne5 looks good in the first couple plies, but gets white mated in 2 >moves. >2) Crafty sees this very fast, and finds a better root move, Nh2, which prevents >the mate. >3) Nh2 fails low in the next iteration, but isn't getting mated. >4) Crafty is searching other moves at that ply to find a "better" root move. >When it gets to Ne5, it practically hangs. Even though it has already >discovered it was Mated in 2 after Ne5 and it took practically zero time to find >it before, this move is searched for a _long_ time at the root, for no apparent >reason. If you have found this to be true, I would have to recomend you showing Bob this. This is something surely he can fix, and might not know about.
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