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Simplify pawnless endgame evaluation

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Retire KmmKm evaluation function. Instead give a very drawish
scale factor when the material advantage is small and not much
material remains.

Retire NoPawnsSF array. Pawnless endgames without a bishop will
now be scored higher. Pawnless endgames with a bishop pair will
be scored lower. The effect of this is hopefully small.

Consistent results both at short TC (fixed games):
ELO: -0.00 +-2.1 (95%) LOS: 50.0%
Total: 40000 W: 7405 L: 7405 D: 25190

And long TC (fixed games):
ELO: 0.77 +-1.9 (95%) LOS: 78.7%
Total: 39690 W: 6179 L: 6091 D: 27420

bench: 7213723
This commit is contained in:
Chris Cain 2014-01-16 21:50:08 +00:00 • committed by Marco Costalba
parent 53ab32ef0b
commit df201175c6
3 changed files with 4 additions and 26 deletions
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1
src/endgame.cpp
View file

@ -349,7 +349,6 @@ Value Endgame<KQKR>::operator()(const Position& pos) const {
/// Some cases of trivial draws
template<> Value Endgame<KNNK>::operator()(const Position&) const { return VALUE_DRAW; }
template<> Value Endgame<KmmKm>::operator()(const Position&) const { return VALUE_DRAW; }
/// KB and one or more pawns vs K. It checks for draws with rook pawns and

1
src/endgame.h
View file

@ -42,7 +42,6 @@ enum EndgameType {
KRKN, // KR vs KN
KQKP, // KQ vs KP
KQKR, // KQ vs KR
KmmKm, // K and two minors vs K and one or two minors
// Scaling functions

28
src/material.cpp
View file

@ -31,9 +31,6 @@ namespace {
const Value MidgameLimit = Value(15581);
const Value EndgameLimit = Value(3998);
// Scale factors used when one side has no more pawns
const int NoPawnsSF[4] = { 6, 12, 32 };
// Polynomial material balance parameters
// pair pawn knight bishop rook queen
@ -62,7 +59,6 @@ namespace {
// Endgame evaluation and scaling functions are accessed directly and not through
// the function maps because they correspond to more than one material hash key.
Endgame<KmmKm> EvaluateKmmKm[] = { Endgame<KmmKm>(WHITE), Endgame<KmmKm>(BLACK) };
Endgame<KXK> EvaluateKXK[] = { Endgame<KXK>(WHITE), Endgame<KXK>(BLACK) };
Endgame<KBPsK> ScaleKBPsK[] = { Endgame<KBPsK>(WHITE), Endgame<KBPsK>(BLACK) };
@ -165,21 +161,6 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
return e;
}
if (!pos.pieces(PAWN) && !pos.pieces(ROOK) && !pos.pieces(QUEEN))
{
// Minor piece endgame with at least one minor piece per side and
// no pawns. Note that the case KmmK is already handled by KXK.
assert((pos.pieces(WHITE, KNIGHT) | pos.pieces(WHITE, BISHOP)));
assert((pos.pieces(BLACK, KNIGHT) | pos.pieces(BLACK, BISHOP)));
if ( pos.count<BISHOP>(WHITE) + pos.count<KNIGHT>(WHITE) <= 2
&& pos.count<BISHOP>(BLACK) + pos.count<KNIGHT>(BLACK) <= 2)
{
e->evaluationFunction = &EvaluateKmmKm[pos.side_to_move()];
return e;
}
}
// OK, we didn't find any special evaluation function for the current
// material configuration. Is there a suitable scaling function?
//
@ -233,17 +214,16 @@ Entry* probe(const Position& pos, Table& entries, Endgames& endgames) {
}
// No pawns makes it difficult to win, even with a material advantage. This
// catches some trivial draws like KK, KBK and KNK
// catches some trivial draws like KK, KBK and KNK and gives a very drawish
// scale factor for cases such as KRKBP and KmmKm (except for KBBKN).
if (!pos.count<PAWN>(WHITE) && npm_w - npm_b <= BishopValueMg)
{
e->factor[WHITE] = (uint8_t)
(npm_w == npm_b || npm_w < RookValueMg ? 0 : NoPawnsSF[std::min(pos.count<BISHOP>(WHITE), 2)]);
e->factor[WHITE] = npm_w < RookValueMg ? 0 : npm_b <= BishopValueMg ? 4 : 12;
}
if (!pos.count<PAWN>(BLACK) && npm_b - npm_w <= BishopValueMg)
{
e->factor[BLACK] = (uint8_t)
(npm_w == npm_b || npm_b < RookValueMg ? 0 : NoPawnsSF[std::min(pos.count<BISHOP>(BLACK), 2)]);
e->factor[BLACK] = npm_b < RookValueMg ? 0 : npm_w <= BishopValueMg ? 4 : 12;
}
if (pos.count<PAWN>(WHITE) == 1 && npm_w - npm_b <= BishopValueMg)