Author: Robert Hyatt
Date: 10:37:47 02/17/98
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On February 17, 1998 at 12:46:39, Bruce Moreland wrote: > >Mine scores Ng3+ as mate in 18 after 40 minutes on a P2/300. > >Which is not to say that this is accurate, or that Ng3+ is best. I'll >let it run longer. > >bruce Aw shit... I didn't look at the output carefully enough. You are correct... I don't have the complete PV as it was terminated by a hash hit, but CB claimed this is a mate in 20. It is *notorious* for finding a slightly longer than optimal mate however, so your 18 could well be correct. I was fooled in that the +7 PV matched the next PV. I didn't notice the mate score as CB doesn't display things like Mat18 and so forth. It shows the integer score... So in this case, Ng3 seems correct, although I'd probably argue that if g3 does produce a score of +12, that's winning too. I despise positions where you can win the queen or you can mate the opponent. Because either wins... This was Harry's favorite position I believe. (Harry Nelson). He liked the way our extensions picked this up in a heartbeat. One has to do with capturing adjacent to the king without being a checking move. These extend (in CB, *not* Crafty) just like checks do, which can be a little dangerous. But at 5M nodes per second, we could spare a few here and there. :) I'm going to try to re-run it on the Cray to get the full PV, then we can compare notes. But I do have a note in my file where Harry gripes about our finding a mate that is too deep, that there is a shorter one available. He "proved" this with human and computer analysis... but at some point, there was a couple of checking moves that could be replaced by a quiet move to shorten the mate. We didn't see that, even with singular extensions... The quiet move pretty well cut everything off short... I used to have a really *really* hard mate in 8 to find. Hard because the first 7 moves were all non-checks. But they were definitely forcing as they would threaten mate. I'm not sure we ever really "solved" that one in any reasonable amount of time. I think one version finally solved it in a minute or two, which seems unreasonable for a mate in 8 using that machine. I'll see if I can find this thing. I also used to have a few ugly positions that would exercise extensions. IE one position where the first 20 plies or so are all forced... each move a check, which also gets that side out of check, and it is the only legal move. This shredded Cray Blitz several times. Each time I'd modify the parallel search, Harry would toss this position at it and it would promptly crash and burn. Obviously singular extensions runs this out *quite* deeply. :)
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