Author: Robert Hyatt
Date: 09:36:45 11/25/97
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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. 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). In my case, yes I have specific knowledge about bishop+wrong rook pawn. And It knows that if the king can reach the queening square it is all over. So it isn't an issue of not capturing those hanging pawns, it is an issue of trying to find a way to capture them and not allowing the white king to reach a1 at the same time. This can only be done by "horizon trickery"... drive the white king away from the corner, then run over and capture the pawns right at the horizon of the search where white doesn't have enough moves to get to a1 and blockade everything. So in my PV's, the pawn captures are always out at the horizon, and deeper searches just push the captures deeper. but they will never really happen...
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