Author: Dann Corbit
Date: 12:43:36 12/25/98
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On December 25, 1998 at 06:30:11, Thom Perry wrote: >On December 23, 1998 at 19:17:32, Dann Corbit wrote: > >>Here is a position that apparently has a lot of mates. Can anyone find a faster >>or better solution than the best of these (two tied at 32748) which is >>guaranteed to win? >>1R1Q4/5k2/p1p1pPb1/P4qp1/B3p3/4P3/5K1P/8 w - - id "C.A.P.47942"; ce 32740; pv >>Ke1 Bh7 Qf8+ Kg6 Qg7+ Kh5 Bd1+ g4 Bxg4+ Qxg4 Qxh7+ Kg5 Rg8+ Kxf6 Qh6+ Ke5 Qh8+ >>Qg7 Qxg7+ Kd6 Rd8+ Kc5 Qd4+ Kb5 Rb8+ Kxa5 Qb4# >>1R1Q4/5k2/p1p1pPb1/P4qp1/B3p3/4P3/5K1P/8 w - - id "C.A.P.47942"; ce 32744; pv >>Ke1 Bh7 Rb7+ Kg6 Qe8+ Kh6 f7 Kh5 f8=Q+ Kg4 Bd1+ Kh3 Qh5+ Kg2 Qe2+ Kg1 Qf1+ Qxf1+ >>Qxf1+ Kxh2 Rxh7+ Kg3 Rh3# >>1R1Q4/5k2/p1p1pPb1/P4qp1/B3p3/4P3/5K1P/8 w - - id "C.A.P.47942"; ce 32748; pv >>Ke1 Bh7 Rb7+ Kg6 Qe8+ Kh6 f7 Kh5 f8=Q+ Kg4 Qxf5+ Kxf5 Rxh7 Ke5 Bb3 Kd6 Qe7+ Ke5 >>Qxe6# >>1R1Q4/5k2/p1p1pPb1/P4qp1/B3p3/4P3/5K1P/8 w - - id "C.A.P.47942"; ce 32748; pv >>Ke1 Bh7 Rb7+ Kg6 Qe8+ Kh6 f7 Kh5 f8=Q+ Kg4 Qxf5+ Bxf5 Bd1+ Kh3 Rb2 Bg4 Qh8+ Bh5 >>Qxh5# > >What do the large ce values in your post mean? In my chess program >(MCP8), the maximum ce value for a position would be the integer >9999 which corresponds to +99.99 which is mate. A value of 9996 would be >+99.96 which is mate-in-4 for the side to move. A value of -0143 would >mean -1.43 which would be a small advantage for the other side. You are using Rebel. It has a non-standard way of describing a checkmate. I sent a bug report to report the defect. Here is the correct nomenclature from the actual PGN Standard: 16.2.5.6: Opcode "ce": centipawn evaluation The opcode "ce" indicates the evaluation of the indicated position in centipawn units. It takes a single operand, an optionally signed integer that gives an evaluation of the position from the viewpoint of the active player; i.e., the player with the move. Positive values indicate a position favorable to the moving player while negative values indicate a position favorable to the passive player; i.e., the player without the move. A centipawn evaluation value close to zero indicates a neutral positional evaluation. Values are restricted to integers that are equal to or greater than -32767 and are less than or equal to 32766. A value greater than 32000 indicates the availability of a forced mate to the active player. The number of plies until mate is given by subtracting the evaluation from the value 32767. Thus, a winning mate in N fullmoves is a mate in ((2 * N) - 1) halfmoves (or ply) and has a corresponding centipawn evaluation of (32767 - ((2 * N) - 1)). For example, a mate on the move (mate in one) has a centipawn evaluation of 32766 while a mate in five has a centipawn evaluation of 32758. A value less than -32000 indicates the availability of a forced mate to the passive player. The number of plies until mate is given by subtracting the evaluation from the value -32767 and then negating the result. Thus, a losing mate in N fullmoves is a mate in (2 * N) halfmoves (or ply) and has a corresponding centipawn evaluation of (-32767 + (2 * N)). For example, a mate after the move (losing mate in one) has a centipawn evaluation of -32765 while a losing mate in five has a centipawn evaluation of -32757. A value of -32767 indicates an illegal position. A stalemate position has a centipawn evaluation of zero as does a position drawn due to insufficient mating material. Any other position known to be a certain forced draw also has a centipawn evaluation of zero.
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