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Add Tord's polynomial material balance

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Use a polynomial weighted evaluation to calculate
material value.

This is far more flexible and elegant then applying
a series of single euristic rules as before.

Also correct a design issue in which we returned two
values, one for middle game and one for endgame, while
instead, because game phase is a function of board
material itself, only one value should be calculated and
used both for mid and end game.

Verified it is equivalent to the tuning branch results with
parameter values sampled after 40.000 games.

After 999 games at 1+0

Mod vs Orig +277 =482 -240 51.85%  518.0/999  +13 ELO

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2009-07-20 09:56:21 +01:00
parent 5600d91cff
commit 044ad593b3
3 changed files with 52 additions and 39 deletions
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66
src/material.cpp
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@@ -40,7 +40,18 @@ namespace {
const Value BishopPairMidgameBonus = Value(109);
const Value BishopPairEndgameBonus = Value(97);
Key KNNKMaterialKey, KKNNMaterialKey;
// Polynomial material balance parameters
const Value RedundantQueenPenalty = Value(320);
const Value RedundantRookPenalty = Value(554);
const int LinearCoefficients[6] = { 1709, -137, -1185, -166, 141, 59 };
const int QuadraticCoefficientsSameColor[][6] = {
{ 0, 0, 0, 0, 0, 0 }, { 33, -6, 0, 0, 0, 0 }, { 29, 269, -12, 0, 0, 0 },
{ 0, 19, -4, 0, 0, 0 }, { -35, -10, 40, 95, 50, 0 }, { 52, 23, 78, 144, -11, -33 } };
const int QuadraticCoefficientsOppositeColor[][6] = {
{ 0, 0, 0, 0, 0, 0 }, { -5, 0, 0, 0, 0, 0 }, { -33, 23, 0, 0, 0, 0 },
{ 17, 25, -3, 0, 0, 0 }, { 10, -2, -19, -67, 0, 0 }, { 69, 64, -41, 116, 137, 0 } };
// Unmapped endgame evaluation and scaling functions, these
// are accessed direcly and not through the function maps.
@@ -50,6 +61,8 @@ namespace {
ScalingFunction<KQKRP> ScaleKQKRP(WHITE), ScaleKRPKQ(BLACK);
ScalingFunction<KPsK> ScaleKPsK(WHITE), ScaleKKPs(BLACK);
ScalingFunction<KPKP> ScaleKPKPw(WHITE), ScaleKPKPb(BLACK);
Key KNNKMaterialKey, KKNNMaterialKey;
}
@@ -261,10 +274,10 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
// Evaluate the material balance
Color c;
const int bishopsPair_count[2] = { pos.piece_count(WHITE, BISHOP) > 1, pos.piece_count(BLACK, BISHOP) > 1 };
Color c, them;
int sign;
Value egValue = Value(0);
Value mgValue = Value(0);
int matValue = 0;
for (c = WHITE, sign = 1; c <= BLACK; c++, sign = -sign)
{
@@ -291,30 +304,37 @@ MaterialInfo* MaterialInfoTable::get_material_info(const Position& pos) {
}
}
// Bishop pair
if (pos.piece_count(c, BISHOP) >= 2)
{
mgValue += sign * BishopPairMidgameBonus;
egValue += sign * BishopPairEndgameBonus;
}
// Knights are stronger when there are many pawns on the board. The
// formula is taken from Larry Kaufman's paper "The Evaluation of Material
// Imbalances in Chess":
// Redundancy of major pieces, formula based on Kaufman's paper
// "The Evaluation of Material Imbalances in Chess"
// http://mywebpages.comcast.net/danheisman/Articles/evaluation_of_material_imbalance.htm
mgValue += sign * Value(pos.piece_count(c, KNIGHT)*(pos.piece_count(c, PAWN)-5)*16);
egValue += sign * Value(pos.piece_count(c, KNIGHT)*(pos.piece_count(c, PAWN)-5)*16);
// Redundancy of major pieces, again based on Kaufman's paper:
if (pos.piece_count(c, ROOK) >= 1)
matValue -= sign * ((pos.piece_count(c, ROOK) - 1) * RedundantRookPenalty + pos.piece_count(c, QUEEN) * RedundantQueenPenalty);
// Second-degree polynomial material imbalance by Tord Romstad
//
// We use NO_PIECE_TYPE as a place holder for the bishop pair "extended piece",
// this allow us to be more flexible in defining bishop pair bonuses.
them = opposite_color(c);
for (PieceType pt1 = NO_PIECE_TYPE; pt1 <= QUEEN; pt1++)
{
Value v = Value((pos.piece_count(c, ROOK) - 1) * 32 + pos.piece_count(c, QUEEN) * 16);
mgValue -= sign * v;
egValue -= sign * v;
int c1, c2, c3;
c1 = sign * (pt1 != NO_PIECE_TYPE ? pos.piece_count(c, pt1) : bishopsPair_count[c]);
if (!c1)
continue;
matValue += c1 * LinearCoefficients[pt1];
for (PieceType pt2 = NO_PIECE_TYPE; pt2 <= pt1; pt2++)
{
c2 = (pt2 != NO_PIECE_TYPE ? pos.piece_count(c, pt2) : bishopsPair_count[c]);
c3 = (pt2 != NO_PIECE_TYPE ? pos.piece_count(them, pt2) : bishopsPair_count[them]);
matValue += c1 * c2 * QuadraticCoefficientsSameColor[pt1][pt2];
matValue += c1 * c3 * QuadraticCoefficientsOppositeColor[pt1][pt2];
}
}
}
mi->mgValue = int16_t(mgValue);
mi->egValue = int16_t(egValue);
mi->value = int16_t(matValue / 16);
return mi;
}