Author: Thom Perry
Date: 21:40:22 12/25/98
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On December 25, 1998 at 15:43:36, Dann Corbit wrote: >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. Wow, this is really a textbook explanation. I have saved your response as a text file for future reference. But in all honesty, I prefer the MCP method of reporting the CE which I can easily visualize with respect to the program's method of reporting the evaluation score during game play (if the feature has been activated) or during analysis.
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