Nimzo
Joined: 15 Mar 2005
Posts: 64
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 Posted: Mon May 09, 2005 5:25 pm Post subject: Tactics |
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Part 7: Tactics
Part 7.1: Fork of pawn
Context: v 2.300 Debug, Level 8, Pondering ON, [x] Show Thinking
SharpChess2.exe menu "Edit" | "Paste FEN position"
or
SharpGenTest.exe
frmGenerator_Load [frmGenerator.cs]
| Code: | sc.LevelDifficulty(8, 120, 16, 8);
strFEN = "r2qkb1r/ppp1pppp/2n1b3/8/B2PP3/5N1P/1P3PP1/R1BQK2R b KQkq - 0 6";
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After the exchange of pawns, Whites have a strong center with the threat of the fork in d5.
Depending of the power of your computer, Blacks could reply Qb6? instead of Bd7.
If necessary reduce the level of difficulty.
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Part 7.1.1: Analysis
The Debug trace shows the Principal Variations v 2.210 at each iteration of depth.
<depth> <PV>: <alpha score>
1 Bc8: 1025, 1 Bf5: 1049, 1 Bd5: 1116, 1 Bb3: 1144
2 Bb3 Bxb3: -2937, 2 Bf5 exf5: -2095
2 Rc8 Bxc6 bxc6 Rxa7: 289
2 Bc4 Bb3 bxc6: 951
3 Bc4 Bxc6 bxc6 Be3: 999
4 Bc4 Ne5 Be6 Nxc6 bxc6 Bxc6: -239
4 Rb8 d5 b5 dxe6 bxa4 Qxa4 fxe6 Qc6: -12
4 f5 exf5 Bxf5 Bxc6 bxc6 O-O: 51
4 Qd6 O-O O-O-O Bb3 Qxc6 Rxa7 Qxe4: 505
5 Qd6 O-O O-O-O Bxc6 Qxc6 Be3 Qe4: 896 overestimation of the position
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With more time sc.LevelDifficulty(11, 120, 40, 32);
Computer could find the correct move Bd7.
6 Qd6 O-O Qd7 Bb5 Qd8 Be3 bxc6: 351
7 Qd6 d5 b5 dxe6 bxa4 exf7 Kxf7 Qxa4 Kg8: -503
7 Bd7 d5 Nb4 Bxd7 Qxd7 O-O c6 Be3 Nc6: 217
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Part 7.1.2: PositionalPoints [PiecePawn.cs]
The evaluation of the threat of the fork by the pawn will accelerate the research of the best move.
The cost is acceptable even when no forks are possible.
| Code: | intPoints += intAdvancementBonus + EvalForkPawn();
return intPoints;
}
} // end PositionalPoints
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Part 7.1.3: EvalForkPawn [PiecePawn.cs]
If a pawn threatens a piece, add a light bonus.
If fork, add the value of the smallest piece.
| Code: | /// <summary>Eval the threat of fork by the pawn</summary>
/// <returns><para>Min of the value of attacked pieces if fork</para>
/// <para>30 if the pawn threatens a piece</para>
/// <para>0 if not threat</para></returns>
private int EvalForkPawn()
{
const int iTHREAT_PAWN = 30; int iBonus = 0; Square sqrLeft, sqrRight; Piece pieceLeft = null;
if ((sqrLeft = Board.GetSquare(m_Base.Square.Ordinal + m_Base.Player.PawnAttackLeftOffset)) != null)
{
pieceLeft = sqrLeft.Piece;
if (pieceLeft != null && pieceLeft.Player.Colour != m_Base.Player.Colour &&
pieceLeft.IsCapturable && pieceLeft.Name != Piece.enmName.Pawn)
iBonus = iTHREAT_PAWN; // see where CanBeDrivenAwayByPawn is called
}
if ((sqrRight = Board.GetSquare(m_Base.Square.Ordinal + m_Base.Player.PawnAttackRightOffset)) != null)
{
Piece pieceRight = sqrRight.Piece;
if (pieceRight != null && pieceRight.Player.Colour != m_Base.Player.Colour &&
pieceRight.IsCapturable && pieceRight.Name != Piece.enmName.Pawn)
iBonus = (iBonus == iTHREAT_PAWN) ? Math.Min(pieceLeft.Value, pieceRight.Value) : iTHREAT_PAWN;
}
return iBonus;
} // end EvalForkPawn
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________________
Part 7.1.4: Analysis with EvalForkPawn
With: sc.LevelDifficulty(8, 120, 16, 8) Principal Variations v 2.210
1 Bc8: 1025, 1 Rc8: 1036, 1 Bd5: 1086, 1 Bb3: 1144 intPoints += intAdvancementBonus + EvalForkPawn();
1 Bc8: 1025, 1 Bf5: 1049, 1 Bd5: 1116, 1 Bb3: 1144 intPoints += intAdvancementBonus; // + EvalForkPawn();
About Bd5: alpha score 1086 = 1116 - 30
2 Bb3 Bxb3: -2937, 2 Bf5 exf5: -2095, 2 Bd5 exd5 Qxd5: -1316
2 Bc4 Bb3 bxc6: 951
3 Bc4 Bxc6 bxc6 Be3: 999
If Bc4?, d5 b5. dxc6 bxa4. Qxd8 Rxd8. Rxa4 Bb3. Rd4 Rxd4. Nxd4 Bc4. Bf4 Kd8. Kd2 +-
4 Bc4 Ne5 Bd5 exd5 Qxd5: -1358 Compare with 4 Bc4 Ne5 Be6 Nxc6 bxc6 Bxc6: -239
4 Bc8 d5 b5 Bxb5 bxa4 Qxa4: -305
4 Qd6 O-O Bc4 Bb3 Qxc6: 290 Compare with 4 Qd6 O-O O-O-O Bb3 Qxc6 Rxa7 Qxe4: 505
4 Bd7 d5 Nb4 O-O: 294
4 Bd7 d5 Nb4 O-O: 294
5 Bd7 d5 Nb8 Bxd7 Nxd7 O-O: 252 estimation more realistic than 5 Qd6 O-O O-O-O Bxc6 Qxc6 Be3 Qe4: 896
Nimzo |
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