Author: Rick Bischoff
Date: 23:29:13 07/19/03
Hi all,
I have a very weird bug in my engine that I can't explain. It was playing on
the ICC tonight and we reached the following position:
r1b1kb1r/pp2pppp/2n2n2/q2p4/3P1B2/2NBP3/PP3PPP/R2QK1NR b KQkq - 0 7
(Ziggy2 is playing black here)... The analysis shows:
1496592 <first : depth: 1 e=35 a5b5
1496592 <first : depth: 2 e=25 a5b6 d3b5
1496592 <first : depth: 3 e=22 a5b6 d3b5 f6e4
1497536 <first : depth: 4 e=8 c8f5 d3f5 a5c3 b2c3
1501437 <first : eval: 8 making move: 0 BISHOP: c8f5
It was considering Qb6 for the first 3 plies, and then... all of a sudden, it
switches to
Bf5?? Bxf5 Qxc3?? bxc3 and gives this a positive evaluation!!?? It just hung
its bishop and queen!! WTF?
Anyway, after the other player gave it a firm beating, I fed the position back
into the engine and got:
depth: 1 e=35 h8g8
depth: 2 e=25 a5b4 a1b1
depth: 3 e=25 a5b4 d1b1 h7h6
depth: 4 e=13 g7g5 f4e5 c6e5 d4e5
depth: 5 e=-15 a5b4 d1b1 h8g8 g1e2 h7h6
depth: 6 e=-25 a5b4 d1c1 c8g4 g1e2 b4b2 c1b2
eval: -25 making move: 0 QUEEN: a5b4
As the analysis... So, it must have been something in the hash tables, right?
Where is this bug likely to be?
(FYI: The search it is using is strictly alpha/beta, check extensions only and
a qsearch with captures only. The eval function is very crude.. material, small
bonus for center control and small bonus for development.)
[Event "ICC 5 0"]
[Site "Internet Chess Club"]
[Date "2003.07.20"]
[Round "-"]
[White "##censored##"]
[Black "Ziggy2"]
[Result "1-0"]
[ICCResult "Black checkmated"]
[WhiteElo "1492"]
[BlackElo "1624"]
[Opening "QGD: Marshall defense"]
[ECO "D06"]
[NIC "QP.08"]
[Time "02:09:24"]
[TimeControl "300+0"]
1. d4 d5 2. c4 Nf6 3. cxd5 c6 4. Nc3 cxd5 5. Bf4 Nc6 6. e3 Qa5 7. Bd3 Bf5 8.
Bxf5 e6 9. Bd3 Rg8 10. Nf3 Bb4 11. Qb3 Bxc3+ 12. bxc3 Ne4 13. Bxe4 dxe4 14.
Ne5 h5 15. Nxc6 bxc6 16. O-O Rd8 17. Qb7 Qb6 18. Rab1 Qxb7 19. Rxb7 f6 20.
Rfb1 a5 21. Rb8 Rxb8 22. Rxb8+ Kf7 23. Rxg8 Kxg8 24. Bd6 Kf7 25. c4 Kg6 26.
c5 Kf5 27. h3 e5 28. dxe5 fxe5 29. Kf1 a4 30. Ke1 g5 31. Kd2 g4 32. hxg4+
hxg4 33. a3 Ke6 34. Kc3 Kf5 35. Kb4 Ke6 36. Kxa4 g3 37. fxg3 Kd7 38. Kb4 Kc8
39. Ka5 Kb7 40. a4 Kc8 41. Kb6 Kd7 42. a5 Ke6 43. Kxc6 Kf6 44. Kd5 Kg5 45.
Bxe5 Kf5 46. c6 Kg6 47. c7 Kf7 48. c8=Q Ke7 49. a6 Kf7 50. a7 Ke7 51. Qc6
Kf8 52. a8=Q+ Ke7 53. Qa7+ Kd8 54. Qca8# {Black checkmated} 1-0
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Last modified: Thu, 15 Apr 21 08:11:13 -0700
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