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evaluate loose pieces
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Gary



Joined: 12 Dec 2006
Posts: 339
PostPost subject: Re: evaluate loose pieces    Posted: Tue Feb 28, 2012 1:35 pm Reply to topic Reply with quote
mcostalba wrote:
A possible implementation of your idea that seems an acceptable compromise between speed and accuracy could be:

Code:

  template<Color Us>
  Score evaluate_threats(const Position& pos, EvalInfo& ei) {

    const Color Them = (Us == WHITE ? BLACK : WHITE);

    Bitboard b, bb;
    Score score = SCORE_ZERO;

    // Enemy pieces not defended by a pawn and under our attack
    Bitboard weakEnemies =  pos.pieces(Them)
                          & ~ei.attackedBy[Them][PAWN]
                          & ei.attackedBy[Us][0];
    if (!weakEnemies)
        return SCORE_ZERO;

    Bitboard undefended = weakEnemies & ~ei.attackedBy[Them][0];

    // Add bonus according to type of attacked enemy piece and to the
    // type of attacking piece, from knights to queens. Kings are not
    // considered because are already handled in king evaluation.
    for (PieceType pt1 = KNIGHT; pt1 < KING; pt1++)
    {
        b = ei.attackedBy[Us][pt1] & weakEnemies;
        if (b)
            for (PieceType pt2 = PAWN; pt2 < KING; pt2++)
                if (bb = b & pos.pieces(pt2), bb)
                    score += bb & undefended ? 2 * ThreatBonus[pt1][pt2]
                                             : 1 * ThreatBonus[pt1][pt2];
    }
    return score;
  }

I gave this idea a try, and it seems that 2x threat bonus is too much. Didn't test too long, but after 150 games, about -40 elo.

Tried a more modest variation of:
Code:

score += bb & undefended ? ((5 * ThreatBonus[pt1][pt2]) / 4)
+                                                                   : ((3 * ThreatBonus[pt1][pt2]) / 4);

And that was:
Score of base vs Stockfish 120227 64bit: 178 - 180 - 635 [0.50] 993
ELO difference: -1

So, no real help Smile. I'll try 1.5x and 0.5x.
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Display posts from previous:   
Subject Author Date/Time
evaluate loose pieces Lucas Braesch Sun Feb 26, 2012 5:20 am
      Re: evaluate loose pieces Larry Kaufman Sun Feb 26, 2012 3:57 pm
            Re: evaluate loose pieces Lucas Braesch Sun Feb 26, 2012 4:11 pm
                  Re: evaluate loose pieces Eelco de Groot Sun Feb 26, 2012 5:57 pm
                        Re: evaluate loose pieces Michael Hoffmann Sun Feb 26, 2012 6:53 pm
                        Re: evaluate loose pieces Marco Costalba Sun Feb 26, 2012 7:04 pm
                              Re: evaluate loose pieces Eelco de Groot Mon Feb 27, 2012 12:46 am
                                    Re: evaluate loose pieces Marco Costalba Mon Feb 27, 2012 7:17 am
                                          Re: evaluate loose pieces Lucas Braesch Mon Feb 27, 2012 10:20 am
                                                Re: evaluate loose pieces Sam Hamilton Mon Feb 27, 2012 10:23 am
                                          Re: evaluate loose pieces Lucas Braesch Mon Feb 27, 2012 1:40 pm
                                                Re: evaluate loose pieces Evert Glebbeek Mon Feb 27, 2012 2:34 pm
                                          Re: evaluate loose pieces Marek Kwiatkowski Mon Feb 27, 2012 2:58 pm
                                          Re: evaluate loose pieces Eelco de Groot Mon Feb 27, 2012 9:45 pm
                                          Re: evaluate loose pieces Gary Tue Feb 28, 2012 1:35 pm
                                                Re: evaluate loose pieces Marek Kwiatkowski Tue Feb 28, 2012 2:35 pm
                                                      Re: evaluate loose pieces Joona Kiiski Tue Feb 28, 2012 4:04 pm
                                                            Re: evaluate loose pieces Marek Kwiatkowski Tue Feb 28, 2012 5:57 pm
                                                            Re: evaluate loose pieces Eelco de Groot Fri May 25, 2012 11:36 pm
                                                      Re: evaluate loose pieces Gary Tue Feb 28, 2012 4:04 pm
                              Re: evaluate loose pieces Lucas Braesch Mon Feb 27, 2012 3:57 am
                        Re: evaluate loose pieces Sam Hamilton Sun Feb 26, 2012 7:12 pm
            Re: evaluate loose pieces Miguel A. Ballicora Sun Feb 26, 2012 5:11 pm
                  Re: evaluate loose pieces Larry Kaufman Sun Feb 26, 2012 5:20 pm
                        Re: evaluate loose pieces Sam Hamilton Sun Feb 26, 2012 6:50 pm
                              Re: evaluate loose pieces Lucas Braesch Mon Feb 27, 2012 3:59 am
                                    Re: evaluate loose pieces Sam Hamilton Mon Feb 27, 2012 4:28 am
                  Re: evaluate loose pieces Ed Schroder Mon Feb 27, 2012 11:42 am
            Re: evaluate loose pieces Gerd Isenberg Sun Feb 26, 2012 7:56 pm
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