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Subject: perpetual check recognition

Author: Andreas Herrmann

Date: 05:49:58 01/30/04


after a good start of a 5:1 over the engine Amateur, my engine blunders again
like in many other games, because of not recognizing perpetual check fast
enough. Most other progs are recognicing a perpetual check faster than my engine
BlackBishop.
Could it be the reason, that my engine does not try check moves in qsearch? In
the search i extend off course the checking moves, but that's not enough, to
recognice perpetual checks fast enough.
I have also tryd a special piece of code to recognice such perpetual checks in
the search, but each time, i thought i have all conditions found for a save
perpetual check detection, i found later another special case. So i have
disabled this code again.
My conditions inside the pertual check line detection are sofar:
- the piece that checks the king can't be captured
- no check moves by pawns inside the line
- no capture moves inside the line
- king in check isn't mated
At the moment i can't find the positions on my hard disc, where this conditions
had been not enough.

[Event "Computer chess game"]
[Site "DUAL"]
[Date "2004.01.30"]
[Round "7"]
[White "Amateur 2.4"]
[Black "BlackBishop 0.9.5z"]
[Result "1/2-1/2"]
[TimeControl "40/180"]

1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6 7. f4 Qb6 8.
Qd2 Qxb2 9. Rb1 Qa3 10. f5 Nc6 11. fxe6 fxe6 12. Nxc6 bxc6 13. e5 dxe5 14.
Bxf6 gxf6 15. Ne4 Be7 16. Be2 h5 17. Rb3 Qa4 18. Nxf6+ Bxf6 19. c4 Bh4+ 20.
g3 Be7 21. O-O h4 22. Bd3 Bc5+ 23. Kh1 Rg8 24. Be2 Bd7 25. Bh5+ Kd8 26. Rb7
Bd4 27. Rf7 c5 28. Rbxd7+ Qxd7 29. Qa5+ Kc8 30. Rxd7 Kxd7 31. Bf7 Rgb8 32.
gxh4 Rb1+ 33. Kg2 Rf8 34. Qa4+ Ke7 35. Bh5 Rc1 36. Qc6 Rf2+ 37. Kg3 Rc3+
38. Kg4 Kf6 39. Bf7 Kxf7 40. Qd7+ Kf8 41. Qd6+ Kf7 42. Qd7+ Kf6 43. Qd8+
Kg7 44. Qe7+ Rf7 45. Qxe6 Rc2 46. a4 Rf4+ 47. Kh5 Rxh2 48. Qg6+ Kf8 49.
Qd6+ Kg7 50. Qg6+ Kf8 51. Qd6+ Ke8 52. Qe6+ Kd8 53. Qd6+ Kc8 54. Qc6+ Kb8
55. Qb6+ Ka8 56. Qc6+ Ka7 57. Qc7+ Ka8 58. Qc8+ Ka7 59. Qc7+ Ka8 60. Qc8+
Ka7 61. Qc7+
{Draw by repetition} 1/2-1/2

I'm not sure which move is here the best to avoid the perpetual check, if it's
not to late at that point:
[d]8/6k1/p3Q3/2p1p2K/P1Pb1r1P/8/2r4P/8 b - - 0 47
At this point, BlackBishop needs 12 plys without my perpetual check detection to
see that Rxh2 is a draw and switched later to Rg2.

ply score   csec     nodes          pv
 5    370      3     15947  5/11/12 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kh7 50.Qg6+
Kh8 51.Qf5  {531kNs 0:00,03}
 6    370      7     34960  6/13/14 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kg7 50.Qe7+
{499kNs 0:00,07}
 7    370     13     69992  7/14/16 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kg7 50.Qe7+
{538kNs 0:00,13}
 8    370     31    176156  8/17/19 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kg7 50.Qe7+
{568kNs 0:00,31}
 9    370     65    370340  9/18/20 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kg7 50.Qe7+
{570kNs 0:00,65}
10    370    155    896383 10/21/22 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kg7 50.Qe7+
{578kNs 0:01,55}
11    370    425   2509633 11/23/24 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kg7 50.Qe7+
{591kNs 0:04,25}
12    370   1287   7622057 12/24/26 47...Rxh2 48.Qe7+ Kg8 49.Qe8+ Kg7 50.Qe7+
{? 592kNs 0:12,87}
12      0   1343   7956261 12/25/27 47...Rxh2 48.Qg6+ Kf8 49.Qd6+ Ke8 50.Qe6+
Kd8 51.Qd6+ Kc8 52.Qc6+ Kd8 53.Qd6+  {592kNs 0:13,43}
12      1   1815  10542378 12/26/27 47...Rf6 48.Qg4+ Kf8 49.Qc8+ Kg7 50.Qg4+ Rg6
 {581kNs 0:18,15}
12    232   7120  38981334 12/26/28 47...Rff2 48.Qg6+ Kf8 49.Qxa6 Rxh2 50.Qf6+
Kg8 51.Qe6+ Kf8 52.Qf6+ Ke8 53.Qe6+ Kd8 54.Qd6+ Kc8 55.Qc6+ Kb8 56.a5 Rxc4
{547kNs 1:11,20}
12    284  11148  61602624 12/28/30 47...Rg2 48.h3 Rf8 49.Qe7+ Rf7 50.Qe6 Rf8
51.Qe7+ Kg8 52.Qe6+ Rf7 53.a5 Rb2 54.Qc8+ Rf8  {553kNs 1:51,48}
13    284  13233  73659325 13/28/30 47...Rg2 48.h3 Rf8 49.Qe7+ Rf7 50.Qe6 Rf8
{557kNs 2:12,33}

How does others recognize draw by perpetual check?
Or is it normal that the checking side finds such pertual check lines faster?
Any comments are welcome.

regards
Andreas







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