Author: Robert Hyatt
Date: 12:14:46 05/30/01
Go up one level in this thread
On May 30, 2001 at 13:23:57, J. Wesley Cleveland wrote: >On May 29, 2001 at 17:19:09, Robert Hyatt wrote: > >>On May 29, 2001 at 14:21:13, Peter Fendrich wrote: >> >>>This position appeared in an ICC game: Guitje - TerraPi >>> >>>[D]2r3kb/5q1p/4pPp1/1p1pP3/p2P2Q1/PrP5/1P3R1R/2B3K1 w - - 0 42 >>> >>>the last move from Terra was 41... b5 >>>Some moves earlier when white made g6, Terra decided to move the bishop from g7 >>>to h8. >>>Both Rb3 and Bh8 are locked in and Terra is absolutely unaware of the >>>hopeless situation. Yes, Terra lost... >>> >>>I see two different but connected problems for computer programs here: >>> - the closed position itself >>> - the two blocked pieces. >>> >>>How do you solve/avoid positions like this? Terra has about equal eval for this >>>position. >>>It is of course possible to punish pawn chains like this in order to avoid >>>closed positions but is that really a solution and how to deal with blocked >>>positions? >>> >>>//Peter >> >> >>First, this looks dead lost. I get big scores (>3) after a few seconds and 13 >>plies. >> >>The position you gave is too late to repair. You have to recognize blocked >>pawns _before_ they are blocked, which means the 'mistakes' were made earlier >>in the game. I evaluate blocked pawns in Crafty, but I also evaluate pawn >>levers and make sure I keep a pawn break opportunity alive to avoid getting >>into totally closed positions... >> >>Here you should probably find Rxh7 is crushing of course... > >I ran this position on crafty 18.3 and got this log. Between plies 13 and 14 >there is an effective branching factor of almost 600. I know that fail highs can >cause big problems, but this seems extreme. > > 13 27.10 3.77 1. Rxh7 Kxh7 2. Qh4+ Kg8 3. Rh2 Bxf6 > 4. exf6 Kf8 5. Qh8+ Qg8 6. Rh7 g5 7. > f7 Qxh8 8. Rxh8+ Kxf7 9. Rxc8 g4 10. > Kf2 Kf6 > 13-> 34.05 3.77 1. Rxh7 Kxh7 2. Qh4+ Kg8 3. Rh2 Bxf6 > 4. exf6 Kf8 5. Qh8+ Qg8 6. Rh7 g5 7. > f7 Qxh8 8. Rxh8+ Kxf7 9. Rxc8 g4 10. > Kf2 Kf6 > 14 43.34 ++ 1. Rxh7!! > 14 335:00 4.30 1. Rxh7 Kxh7 2. Qh4+ Kg8 3. Rh2 Bxf6 > 4. exf6 Kf8 5. Qh8+ Qg8 6. f7 Qxh8 > 7. Rxh8+ Kxf7 8. Rxc8 Kf6 9. Kg2 Kf5 > 10. Rf8+ Ke4 11. Rf4+ Kd3 12. Rf3+ > Ke4 13. Kg3 > 14-> 335:22 4.30 1. Rxh7 Kxh7 2. Qh4+ Kg8 3. Rh2 Bxf6 > 4. exf6 Kf8 5. Qh8+ Qg8 6. f7 Qxh8 > 7. Rxh8+ Kxf7 8. Rxc8 Kf6 9. Kg2 Kf5 > 10. Rf8+ Ke4 11. Rf4+ Kd3 12. Rf3+ > Ke4 13. Kg3 This is probably the result of lots of things. 1. hash too small. at 1M nodes per second, you just searched 335*60*1M nodes. it probably was like searching with no hash at all; 2. a fail high means something unexpected happened. Move ordering is therefore shot to hell since what you thought was right is now wrong and vice-versa. 3. When I fail high, I just relax beta to +infinity, rather than the tiered approach I used in Cray Blitz. If there are lots of mates here, that are not forced, the program still has to search them all out as with +infinity, you get zero beta cutoffs at positions where white is to move, until you establish a better beta value after a lot of searching.
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