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'''[[Main Page|Home]] * [[Evaluation]] * Evaluation Function Draft'''
This page is meant to show an example of a relatively simple evaluation function. It is designed specifically for those who have good programming skills but want to get some ideas about chess knowledge required to attain a reasonable playing strength.
=Features=
Proposed evaluation function should deal with the following issues
* [[Material]] (together with some scaling and additional clauses)
* [[Piece-Square Tables]]
* Special case code to deal with the [[Trapped Pieces|trapped pieces]]
* Basic knowledge of [[Pawn Structure|pawn structure]] - [[Doubled Pawn|doubled]], [[Isolated Pawn|isolated]], [[Backward Pawn|backward]] and [[Passed Pawn|passed pawns]]
* Something resembling [[King Safety|king safety]] - [[King Safety#PawnShield|pawn shield]] and [[King Safety#KingTropism|king tropism]] results scaled against the strength of opponent's remaining pieces
* basic knowledge about [[Endgame|endgames]] drawn by [[Material#InsufficientMaterial|insufficient material]]
=Prequisites=
Throughout the draft it will be assumed that the program has the following capabilities
* While [[Make Move|making]] and [[Unmake Move|unmaking]] [[Moves|moves]], it [[Incremental Updates|updates]] the material score for each side, subdivided to pieces and pawns
* It updates the value derived from the piece-square tables for all pieces except the king in the same manner
* When asked, it can return the position of either king
* When asked, it can return the number of white/black pawns, bishops, knights or rooks
* It possesses a function <code>int isPiece(int cl, int sq, int pc)</code>, returning 1 if a piece pc of color cl stands on the square sq and 0 otherwise.
=Initialization=
<span id="Distance"></span>
==Distance==
When the program is turned on, it must fill the tables with bonuses for [[Distance|distance]] between any two squares that will be used for evaluating [[King Safety#KingTropism|king tropism]]. The following formula is borrowed from the masters thesis by [[Adam Kujawski]] <ref>[[Adam Kujawski]] ('''1994'''). ''Programowanie gry w szachy''. Masters thesis, [[University of Warsaw]], [http://www.armageddon.szach.pl/joanna.pdf pdf] (Polish)</ref> and modified in such a way that all the scores become positive. It assumes that both rows and columns are numbered from 0 to 7 and that we have a function "abs" returning the value without the sign.
<pre>
/* initializes the table of distances between squares */
void setDist() {
int i,j;
for (i = 0; i < 64; ++i) {
for (j = 0; j < 64; ++j) {
dist_bonus[i][j] = 14 - ( abs ( COL(i) - COL(j) )
+ abs ( ROW(i) - ROW(j) ) );
}
}
}
</pre>
Taking this function as a basis, tropism tables for various piece types will be derived within its body, just after determining the value of dist_bonus[i][j].
<pre>
qk_dist[i][j] = (dist_bonus[i][j] * 5) / 2;
rk_dist[i][j] = dist_bonus[i][j] / 2;
nk_dist[i][j] = dist_bonus[i][j];
</pre>
At the beginning we can assume that bk_dist is equal to rk_dist, but there is a better idea, taking into account the relevance of a [[Diagonal|diagonal]]. To apply it, we need two tables numbering the diagonals and [Anti-Diagonals|anti-diagonals].
<pre>
int diag_nw[64] = {
0, 1, 2, 3, 4, 5, 6, 7,
1, 2, 3, 4, 5, 6, 7, 8,
2, 3, 4, 5, 6, 7, 8, 9,
3, 4, 5, 6, 7, 8, 9,10,
4, 5, 6, 7, 8, 9,10,11,
5, 6, 7, 8, 9,10,11,12,
6, 7, 8, 9,10,11,12,13,
7, 8, 9,10,11,12,13,14
};
int diag_ne[64] = {
7, 6, 5, 4, 3, 2, 1, 0,
8, 7, 6, 5, 4, 3, 2, 1,
9, 8, 7, 6, 5, 4, 3, 2,
10, 9, 8, 7, 6, 5, 4, 3,
11,10, 9, 8, 7, 6, 5, 4,
12,11,10, 9, 8, 7, 6, 5,
13,12,11,10, 9, 8, 7, 6,
14,13,12,11,10, 9, 8, 7
};
</pre>
Now we have to incorporate the following code
<pre>
int bonus_dia_distance[15] = {5, 4, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
kb_dist [i][j] += bonus_dia_distance[abs(diag_ne[i] - diag_ne[j])];
kb_dist [i][j] += bonus_dia_distance[abs(diag_nw[i] - diag_nw[j])];
</pre>
==Others==
At the initialization stage, we also count the value of INITIAL_PIECE_MATERIAL. It will be needed in scaling the king safety values against the remaining enemy material. We want it to be calculated rather than to become a constant because different piece values might be used by the program.
Here You can view the complete proposal of the [[Initialization Routine|initialization routine]].
<span id="KingSafety"></span>
=King Safety=
Our simple King safety routine works as follows: evaluating each piece we update two variables: <span style="background-color: #bcbcbc; font-family: "Courier New",Courier,monospace;">tropismToWhiteKing</span> and <span style="background-color: #bcbcbc; font-family: "Courier New",Courier,monospace;">tropismToBlackKing</span>, feeding them with the values from the distance tables (see initialization for their details). Then the pawn shield value is computed (I'd like it to be 0 for a complete pawn shield, growing negative as defects accumulate). Finally, the following formula is applied:
<pre>
whiteKingSafety = ( (whiteKingShield - tropismToWhiteKing) * blackPieceMaterial ) / INITIAL_PIECE_MATERIAL;
blackKingSafety = ( (blackKingShield - tropismToBlackKing) * whitePieceMaterial ) / INITIAL_PIECE_MATERIAL;
</pre>
=References=
<references />
'''[[Evaluation|Up one Level]]'''
This page is meant to show an example of a relatively simple evaluation function. It is designed specifically for those who have good programming skills but want to get some ideas about chess knowledge required to attain a reasonable playing strength.
=Features=
Proposed evaluation function should deal with the following issues
* [[Material]] (together with some scaling and additional clauses)
* [[Piece-Square Tables]]
* Special case code to deal with the [[Trapped Pieces|trapped pieces]]
* Basic knowledge of [[Pawn Structure|pawn structure]] - [[Doubled Pawn|doubled]], [[Isolated Pawn|isolated]], [[Backward Pawn|backward]] and [[Passed Pawn|passed pawns]]
* Something resembling [[King Safety|king safety]] - [[King Safety#PawnShield|pawn shield]] and [[King Safety#KingTropism|king tropism]] results scaled against the strength of opponent's remaining pieces
* basic knowledge about [[Endgame|endgames]] drawn by [[Material#InsufficientMaterial|insufficient material]]
=Prequisites=
Throughout the draft it will be assumed that the program has the following capabilities
* While [[Make Move|making]] and [[Unmake Move|unmaking]] [[Moves|moves]], it [[Incremental Updates|updates]] the material score for each side, subdivided to pieces and pawns
* It updates the value derived from the piece-square tables for all pieces except the king in the same manner
* When asked, it can return the position of either king
* When asked, it can return the number of white/black pawns, bishops, knights or rooks
* It possesses a function <code>int isPiece(int cl, int sq, int pc)</code>, returning 1 if a piece pc of color cl stands on the square sq and 0 otherwise.
=Initialization=
<span id="Distance"></span>
==Distance==
When the program is turned on, it must fill the tables with bonuses for [[Distance|distance]] between any two squares that will be used for evaluating [[King Safety#KingTropism|king tropism]]. The following formula is borrowed from the masters thesis by [[Adam Kujawski]] <ref>[[Adam Kujawski]] ('''1994'''). ''Programowanie gry w szachy''. Masters thesis, [[University of Warsaw]], [http://www.armageddon.szach.pl/joanna.pdf pdf] (Polish)</ref> and modified in such a way that all the scores become positive. It assumes that both rows and columns are numbered from 0 to 7 and that we have a function "abs" returning the value without the sign.
<pre>
/* initializes the table of distances between squares */
void setDist() {
int i,j;
for (i = 0; i < 64; ++i) {
for (j = 0; j < 64; ++j) {
dist_bonus[i][j] = 14 - ( abs ( COL(i) - COL(j) )
+ abs ( ROW(i) - ROW(j) ) );
}
}
}
</pre>
Taking this function as a basis, tropism tables for various piece types will be derived within its body, just after determining the value of dist_bonus[i][j].
<pre>
qk_dist[i][j] = (dist_bonus[i][j] * 5) / 2;
rk_dist[i][j] = dist_bonus[i][j] / 2;
nk_dist[i][j] = dist_bonus[i][j];
</pre>
At the beginning we can assume that bk_dist is equal to rk_dist, but there is a better idea, taking into account the relevance of a [[Diagonal|diagonal]]. To apply it, we need two tables numbering the diagonals and [Anti-Diagonals|anti-diagonals].
<pre>
int diag_nw[64] = {
0, 1, 2, 3, 4, 5, 6, 7,
1, 2, 3, 4, 5, 6, 7, 8,
2, 3, 4, 5, 6, 7, 8, 9,
3, 4, 5, 6, 7, 8, 9,10,
4, 5, 6, 7, 8, 9,10,11,
5, 6, 7, 8, 9,10,11,12,
6, 7, 8, 9,10,11,12,13,
7, 8, 9,10,11,12,13,14
};
int diag_ne[64] = {
7, 6, 5, 4, 3, 2, 1, 0,
8, 7, 6, 5, 4, 3, 2, 1,
9, 8, 7, 6, 5, 4, 3, 2,
10, 9, 8, 7, 6, 5, 4, 3,
11,10, 9, 8, 7, 6, 5, 4,
12,11,10, 9, 8, 7, 6, 5,
13,12,11,10, 9, 8, 7, 6,
14,13,12,11,10, 9, 8, 7
};
</pre>
Now we have to incorporate the following code
<pre>
int bonus_dia_distance[15] = {5, 4, 2, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
kb_dist [i][j] += bonus_dia_distance[abs(diag_ne[i] - diag_ne[j])];
kb_dist [i][j] += bonus_dia_distance[abs(diag_nw[i] - diag_nw[j])];
</pre>
==Others==
At the initialization stage, we also count the value of INITIAL_PIECE_MATERIAL. It will be needed in scaling the king safety values against the remaining enemy material. We want it to be calculated rather than to become a constant because different piece values might be used by the program.
Here You can view the complete proposal of the [[Initialization Routine|initialization routine]].
<span id="KingSafety"></span>
=King Safety=
Our simple King safety routine works as follows: evaluating each piece we update two variables: <span style="background-color: #bcbcbc; font-family: "Courier New",Courier,monospace;">tropismToWhiteKing</span> and <span style="background-color: #bcbcbc; font-family: "Courier New",Courier,monospace;">tropismToBlackKing</span>, feeding them with the values from the distance tables (see initialization for their details). Then the pawn shield value is computed (I'd like it to be 0 for a complete pawn shield, growing negative as defects accumulate). Finally, the following formula is applied:
<pre>
whiteKingSafety = ( (whiteKingShield - tropismToWhiteKing) * blackPieceMaterial ) / INITIAL_PIECE_MATERIAL;
blackKingSafety = ( (blackKingShield - tropismToBlackKing) * whitePieceMaterial ) / INITIAL_PIECE_MATERIAL;
</pre>
=References=
<references />
'''[[Evaluation|Up one Level]]'''
