I found a new set of PST values ("Chili") that causes MinimalChess to play significantly better than Salsa (+36 ELO) and even appears stronger than Pesto (+21 ELO) in my tests!
I really like these "Chili" PSTs. Pesto plays really strong against Bit-Genie_2 (71.6%) but surprisingly weak against dumber-1.2 (44.1%) whereas the spread with the Chili tables compared to the same opponents is much smaller. (49.5% to 69.0%) It plays decent openings even without an opening book and it manages to convert won endgames as far as I can see!
Code: Select all
public static int LostValue => -9999;
static readonly int[] PhaseValues = new int[6] { 0, 155, 305, 405, 1050, 0 };
static readonly int Midgame = 5255;
static readonly int Endgame = 435;
static readonly int[,] MidgameTables = new int[6, 64]{
{ //PAWN MG
100, 100, 100, 100, 100, 100, 100, 100,
173, 227, 144, 189, 182, 228, 124, 75,
82, 94, 111, 115, 152, 150, 109, 68,
65, 95, 87, 102, 104, 92, 98, 59,
52, 80, 77, 92, 96, 86, 90, 55,
55, 79, 77, 70, 83, 82, 114, 69,
45, 80, 61, 56, 64, 102, 116, 59,
100, 100, 100, 100, 100, 100, 100, 100,
},
{ //KNIGHT MG
106, 248, 280, 272, 326, 196, 291, 178,
224, 255, 369, 322, 319, 360, 307, 289,
254, 365, 342, 368, 387, 423, 380, 344,
296, 322, 322, 357, 343, 378, 324, 325,
292, 313, 320, 317, 333, 326, 326, 299,
283, 298, 317, 317, 326, 323, 329, 290,
277, 254, 294, 303, 304, 325, 295, 290,
214, 284, 251, 273, 289, 281, 288, 278,
},
{ //BISHOP MG
275, 319, 255, 290, 292, 289, 316, 307,
301, 344, 312, 314, 354, 382, 347, 287,
316, 357, 377, 366, 355, 374, 364, 334,
330, 337, 350, 378, 370, 373, 339, 330,
327, 349, 345, 357, 365, 344, 341, 336,
333, 349, 345, 347, 344, 359, 347, 340,
339, 346, 348, 331, 340, 352, 363, 335,
304, 331, 318, 315, 321, 321, 301, 308,
},
{ //ROOK MG
504, 520, 493, 517, 519, 493, 489, 500,
501, 506, 538, 535, 545, 538, 491, 507,
477, 503, 506, 506, 495, 523, 529, 488,
452, 473, 485, 509, 501, 512, 475, 460,
445, 456, 472, 477, 483, 472, 490, 457,
437, 461, 465, 460, 479, 473, 475, 446,
435, 467, 461, 468, 476, 487, 475, 409,
460, 466, 480, 488, 489, 476, 447, 454,
},
{ //QUEEN MG
854, 910, 921, 913, 955, 939, 928, 926,
881, 867, 910, 921, 898, 961, 936, 948,
894, 896, 916, 921, 939, 969, 954, 960,
879, 880, 898, 894, 907, 925, 904, 904,
897, 881, 897, 896, 904, 904, 910, 905,
890, 908, 898, 903, 901, 908, 917, 911,
872, 893, 917, 906, 912, 919, 903, 908,
903, 888, 897, 915, 891, 879, 875, 858,
},
{ //KING MG
-6, 46, 33, 22, -26, -14, 14, 12,
23, 11, 22, 20, 11, 5, -10, -25,
23, 22, 30, 6, 10, 29, 28, -4,
-1, -4, 5, -12, -11, -11, -5, -38,
-15, 8, -18, -40, -53, -36, -27, -46,
6, 1, -37, -73, -80, -54, -20, -21,
12, 11, -10, -74, -52, -20, 16, 18,
-12, 44, 19, -66, 6, -29, 32, 24,
}
};
static int[,] EndgameTables = new int[6, 64]{
{ //PAWN EG
100, 100, 100, 100, 100, 100, 100, 100,
269, 260, 245, 222, 230, 218, 253, 274,
183, 190, 174, 158, 145, 141, 172, 173,
124, 117, 106, 98, 92, 97, 110, 108,
106, 102, 89, 86, 87, 85, 96, 91,
96, 100, 85, 94, 92, 89, 92, 84,
106, 102, 99, 101, 103, 93, 96, 86,
100, 100, 100, 100, 100, 100, 100, 100,
},
{ //KNIGHT EG
225, 237, 268, 249, 258, 250, 220, 190,
254, 273, 265, 283, 276, 261, 261, 234,
257, 265, 293, 292, 281, 279, 264, 246,
265, 284, 303, 302, 302, 293, 286, 266,
265, 274, 296, 305, 297, 297, 286, 263,
261, 277, 281, 294, 290, 280, 265, 260,
245, 260, 271, 276, 278, 262, 258, 239,
246, 236, 258, 264, 261, 262, 238, 225,
},
{ //BISHOP EG
287, 278, 286, 287, 292, 287, 286, 277,
290, 295, 304, 286, 296, 288, 294, 284,
298, 292, 297, 298, 300, 304, 299, 297,
295, 307, 308, 308, 309, 306, 298, 298,
291, 298, 309, 314, 304, 307, 295, 289,
285, 296, 305, 307, 310, 300, 294, 285,
283, 285, 292, 298, 302, 289, 288, 271,
275, 290, 279, 291, 289, 283, 290, 284,
},
{ //ROOK EG
510, 506, 516, 514, 512, 507, 506, 505,
508, 510, 507, 509, 497, 501, 506, 504,
502, 503, 504, 504, 500, 493, 494, 495,
501, 498, 509, 497, 499, 497, 494, 499,
498, 501, 503, 500, 494, 491, 488, 486,
492, 495, 491, 496, 489, 486, 488, 482,
491, 489, 495, 498, 490, 488, 485, 493,
491, 499, 500, 500, 497, 491, 497, 480,
},
{ //QUEEN EG
919, 932, 941, 942, 940, 933, 924, 941,
895, 935, 936, 947, 971, 932, 932, 907,
895, 913, 917, 958, 957, 935, 927, 909,
920, 935, 927, 955, 971, 950, 970, 943,
892, 945, 934, 963, 948, 944, 948, 931,
906, 887, 924, 916, 922, 926, 923, 916,
899, 899, 881, 898, 900, 888, 880, 878,
885, 890, 885, 869, 910, 886, 900, 878,
},
{ //KING EG
-71, -40, -23, -25, -12, 12, 2, -14,
-13, 13, 6, 10, 11, 29, 19, 11,
3, 14, 16, 10, 13, 35, 37, 8,
-13, 16, 19, 22, 19, 27, 22, 1,
-24, -7, 16, 21, 24, 19, 6, -14,
-24, -7, 10, 20, 24, 17, 7, -11,
-31, -13, 3, 11, 12, 3, -7, -21,
-56, -39, -25, -11, -28, -14, -29, -51,
}};
private static int PieceTableIndex(Piece piece) => ((int)piece >> 2) - 1;
//a black piece has 2nd bit set, white has not. Square ^ 56 flips the file, so that tables work for black
private static int SquareTableIndex(int square, Piece piece) => square ^ (28 * ((int)piece & 2));
public static int Evaluate(Board board)
{
int midGame = 0;
int endGame = 0;
int phase = 0;
for (int i = 0; i < 64; i++)
{
Piece piece = board[i];
if (piece == Piece.None)
continue;
Color color = Pieces.GetColor(piece);
int pieceIndex = PieceTableIndex(piece);
int squareIndex = SquareTableIndex(i, piece);
phase += PhaseValues[pieceIndex];
midGame += (int)color * MidgameTables[pieceIndex, squareIndex];
endGame += (int)color * EndgameTables[pieceIndex, squareIndex];
}
double factor = Linstep(Endgame, Midgame, phase);
double score = factor * midGame + (1 - factor) * endGame;
return (int)score;
}
public static double Linstep(double edge0, double edge1, double v)
{
return Math.Min(1, Math.Max(0, (v - edge0) / (edge1 - edge0)));
}
/*
Mean squared error of 'chillipepper003' evaluating 725000 positions from "quiet-labeled.epd"
105609| +0.396856 | 100% Midgame
28134| +0.309630 |
26512| +0.306764 |
28655| +0.310108 |
35035| +0.273508 |
41092| +0.247912 |
54940| +0.232401 |
92300| +0.198270 |
116183| +0.174543 |
196540| +0.203038 | 100% Endgame
------------------------
| +0.246433
*/
Iterate over each square of the board and compute a midGame, endGame and phase value for that particular position. The midGame score is calulated by looking up the value of each encountered piece from the midgame tables and summing them. The endGame score does the same but looks up the values from the endgame tables. The phase value doesn't care about the color or square a piece is found on. Each piece is worth a certain amount of phase points taken from the PhaseValues array.
Now, to reach the final score you mix endGame and midGame score together based on the phase value. Everything above 5255 phase points is 100% midGame, everything below 435 phase points is 100% endGame. And everything in between gets linearly interpolated.
I also like how the values of each piece all average pretty much around the traditional values (1, 3, 3, 5, 9) because it makes it much easier for me to reason about what I see in the tables!
Feel free to give my above tables a try if you rather want to leave the well trodden path!
My engine is published under the MIT license and the only condition that license imposes is to add a License and Copyright Notice.
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