Author: Chris Whittington
Date: 10:04:41 11/25/97
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On November 25, 1997 at 12:40:20, Robert Hyatt wrote: >On November 25, 1997 at 05:10:27, Chris Whittington wrote: > >> >>On November 25, 1997 at 02:29:28, Howard Exner wrote: >> >>>On November 24, 1997 at 13:26:16, Robert Hyatt wrote: >>> >>> >>>>In light of my testing, I'd simply call this a "broken" test position >>>>and >>>>throw it out. Anything but the knight sac loses outright, and most >>>>programs >>>>that can reach reasonable depth see this. I'd bet Fritz finds it quite >>>>quickly as well. But the solution is wrong, because the goal of the >>>>test >>>>was to test knowledge to see if a program could recognize that this is a >>>>draw. To do so requires an evaluation of 0.00, not -3. something, >>>>because >>>>there are plenty of -3 positions that are still dead lost. >>>> >>>>The point here, then, is only to search deeply enough to see that this >>>>move >>>>is the only way to avoid scores of -4 and worse. I ran it on Cray Blitz >>>>and >>>>it found this in 8 seconds, and liked the knight sac from then on. But >>>>the >>>>score never went above -3.8 or so, although I only let it search to >>>>depth=21. >>>>It averaged about 9.7 million nodes per second for comparison, but never >>>>had >>>>a clue that this was drawn, just that it was playing the only move that >>>>didn't >>>>lose within its horizon. (I don't have the output in front of me, but >>>>believe >>>>it found the knight sac at depth=16 or perhaps 17. I can rerun it if >>>>this is >>>>important... >>>> >>>> >>>>I don't count such "solutions" since I know that for every such lucky >>>>correct >>>>find, there are hundreds where such a knight sac only makes things >>>>easier for >>>>the opponent... >>> >>>Yes I agree about the knight sac could make things worse but does >>>that apply to the dynamics of this type of position, namely the >>>wrong bishop theme? What puzzles me on this position is that your >>>program and I assume others would avoid capturing the pawns as you >>>have noted. So the programs somehow "know" half the truth of this >>>draw. The other half would be to "know" that the captures are essential >>>to win. >> >>I agree. This is clearly a very interesting position that throws much >>light on knowledge/search debate. >> >>To 'throw it out' as Bob suggests is a travesty. Presumably allowing the >>one-eyed man to carry on being king in the land of the blind. >> >>But to give a 1 or a 0 for 'solving' it, is also a travesty. > > >I say throw it out because it can be "solved" without being *solved*. >That >is, Na5 is the only move that doesn't lose, when the search is fast >enough >and deep enough to see why. So the right move is forced to avoid >losing, >which is *not* a knowledge test at all. Now if we change the nature of >the >solution so that the evaluation mst be 0.00 (or whatever your normal >draw >score is) then that would change things a lot. But as it is, it can be >solved but not really *solved*... Absolutely agreed. What's needed is a comment on the position to say that only Na5 with a draw evaluation woudl be accepted as a solution, Then the test moves on from being a materialistic 1 or -1, to some sort of quality test. In fact we'ld need to adjust the idea of the 0.00 score, because a program could do, say: Na1 -4.00 150 secs Na5 fail high >= -3.4 200 secs Na5 0.00 350 secs wher it would be apparent that the fail high at -3.4 was actually a solution. Gets complex, no ? :) Also my program doesn't score draws at 0.00. It can make them +ve or -ve at will, depending on circumstances. Generally I (or Thorsten) know when a draw score is output, but this tends to be intuitive. Chris Whittington > >> >>This is one of those positions meriting a 'describe in no less than 300 >>words' answer. >> >>Chris Whittington >> >>> Is it possible to code in some kind of aggressive deep search >>>extension for these captures. In a sense a kind of knowledge that says >>>"now it is the time to search deeply". >>> >>>Like you I am curious on how the "solvers" of this position >>>eval it. What is clear though is that Na5 is much much better than >>>Na1 (the only other alternative).
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