Author: Robert Hyatt
Date: 06:09:28 09/28/98
Go up one level in this thread
On September 27, 1998 at 23:13:51, David Eppstein wrote: >On September 27, 1998 at 09:38:30, Vincent Lejeune wrote: >>[Event "ICS Rated blitz match"] >>[Site "chessclub.com"] >>[Date "1998.08.09"] >>[Round "-"] >>[White "Good-Boy"] >>[Black "singacrafty"] >>[Result "*"] >>[WhiteElo "2914"] >>[BlackElo "2855"] >>[TimeControl "120+8"] >> >>1. e4 c5 2. c3 e6 3. d4 d5 4. e5 cxd4 5. cxd4 Nc6 6. Nf3 Nge7 7. Na3 Nf5 8. >>Nc2 Be7 9. Bd3 Qb6 10. g4 Nh4 11. Nxh4 Bxh4 12. O-O f6 13. g5 Bxg5 14. Qh5+ >>Kf8 15. f4 Bh6 16. exf6 Qc7 17. f5 Bxc1 18. fxe6 Bxe6 19. fxg7+ Kxg7 20. >>Raxc1 Bf7 21. Qg5+ Bg6 22. Qf6+ Kg8 23. Bf5 Nd8 24. Bc8 Nf7 25. Nb4 Qd8 26. >>Nxd5 Qxf6 27. Nxf6+ Kg7 28. Bxb7 Rad8 29. Nd5 Nd6 30. Rc7+ Kh6 31. Bc6 Nf5 >>32. Rxa7 Nxd4 33. Bb7 Rd7 34. Rd1 Nf3+ 35. Kg2 Rg7 36. Kf2 Ne5 37. Ke3 Rb8 >>38. b4 Rgxb7 39. Rxb7 Rxb7 40. a4 Bf7 41. Ke4 Bxd5+ 42. Rxd5 Nc4 43. b5 Ra7 >>44. b6 Rxa4 45. Kd3 Na5 46. Rd6+ Kg5 47. Rd7 Nc6 48. Rxh7 Rb4 49. Rb7 Rh4 >>50. Rc7 Nb4+ 51. Ke2 Rxh2+ 52. Kf3 Rh3+ 53. Kg2 Rb3 54. b7 Na6 55. Rc6 Nb8 > >This is one of those give-away only-a-computer-could-be-this-stupid moves, >right? The best black can hope for by playing Nb8 is to eventually win a pawn >and be in a drawn KRN-KR endgame, but the downside is (as happens below) losing >because the pawn eventually queens. Why not play 55...Rb7 and draw immediately? > turns out that Nb8 is a dead draw, as confirmed by running to huge depth using tablebases. singacrafty probably "cheated" and didn't download *all* the databases, which will *not* work. But crafty, on my machine, sees this as a draw by 5 plies or so, for *either* move... >I do understand why a computer might play this: if it follows the orthodox >material-count plus positional terms eval, a knight might be worth more than an >isolated passed pawn, maybe even one as far advanced as this. The quick fix is >to add a little code to somehow tweak the eval of these KRN-KRP positions to be >nonpositive, so the draw looks good. it's not that at all. Nb8 comes up 0.00 due to databases, and it is seen as a draw before the rook move is followed to a draw as well, and as we know, alpha/beta takes the *first* move with an equal score. > >I think a more principled approach would be to have an eval that gives you >explicit and separate probabilities of various game-ending events: >What are the probabilities that black or white wins by a quick checkmate or >decisive combination? That black or white can force a repetition draw? >That (if the game reaches an endgame) white or black will win there? >The overall eval would then be a simple nonlinear combination of these >probabilities (just the expected value of the overall game). > >I don't see why this approach should be any slower than the orthodox one, since >it is again just a simple numerical combination of the same sorts of eval terms. >But it should have two big advantages: you can measure how often the events >actually occur, and tune your eval accordingly, and you can correctly judge >sacrifices or positions like this where material-count is just wrong. >A third less important advantage is that by changing the combination formula, >you could make the program play appropriately in must-win or must-draw >tournament situations. the problem is that alpha/beta only will use *one* value. So you have to figure out which one to use, or how to combine all of them into one large score. And that can be a problem... > >By the way, who is good-boy? no idea, but *very* strong. A human that uses one or more computer programs to help him. > >>56. Rc7 Rb2+ 57. Kf3 Kf6 58. Ke4 Rb4+ 59. Kd5 Na6 60. Rh7 Rb5+ 61. Kc6 Rb2 >>62. Rh6+ Kg7 63. Rd6 Kf7 64. Rd7+ Ke6 65. Rg7 Rc2+ 66. Kb5 Nb8 67. Rg4 Kf7 >>68. Rc4 Rb2+ 69. Rb4 Rd2 70. Kc4 Kf6 71. Rb5 Rc2+ 72. Kd3 Rc1 73. Ke4 Re1+ >>74. Kf4 Rf1+ 75. Kg4 Rc1 76. Kf3 Ke6 77. Ke4 Re1+ 78. Kf4 Kd6 79. Rb4 Kd5 >>80. Rb6 Re4+ 81. Kf5 Re2 82. Kf6 Re3 83. Rb1 Rd3 84. Kf5 Rd2 85. Kf4 Kd4 >>86. Rb4+ Kd3 87. Ke5 Kc3 88. Rb5 Kc4 89. Rb1 Rc2 90. Kd6 Kd3 91. Kd5 Rd2 >>92. Rb3+ Kc2+ 93. Kc4 Rd8 94. Rb5 Rd6 95. Kc5 Rf6 96. Kd4 Rf4+ 97. Ke5 Rc4 >>98. Kd5 Ra4 99. Kd6 Rg4 100. Kc7 Rg8 101. Ra5 Kc3 102. Ra8 Kd4 103. Rxb8 >>Rg7+ 104. Kb6 Rg6+ 105. Ka7 Rg7 106. Rd8+ Kc5 107. Ka8 Rg1 108. b8=Q Ra1+ >>109. Kb7 Rb1+ 110. Kc7 Rxb8 111. Kxb8 Kc4 112. Kb7 Kc5 113. Rd7 Kb4 114. >>Rc7 Kb5 115. Rc1 Kb4 116. Kb6 Kb3 >>*
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