Basic Lone King Mates?

[Steve Maughan]

Just a quick update. Many thanks to all those who replied. Monarch can now mate a lone king with Q, R, B+B and B+N. It was an interesting exercise and a little more complex than I had imagined. For those that are interested my solution only used a bonus for the aggressor's king in the centre and a penalty for the lone king in the center, with additional smaller penalties for incorrect corner in the case of B+N.

Steve

[H.G.Muller]

And how deep does the search have to be to find these mates, with such an evaluation?

[Tord Romstad]

And how deep does the search have to be to find these mates, with such an evaluation?

My program needs 5 plies of search to win KBN vs K against Fruit 2.1. I am not sure 5 plies would be enough to win against TB defence, but I would be surprised if one or two extra plies would not be sufficient. Even at 7 plies, the whole game takes less than 5 seconds, so I don't consider it a problem.

I use the following very simple eval for KBN vs K:

Code: Select all

int DistanceBonus[8] = {0, 0, 100, 80, 60, 40, 20, 10};

uint8 KBNKtable[128] = {
  200, 190, 180, 170, 160, 150, 140, 130, 0, 0, 0, 0, 0, 0, 0, 0,
  190, 180, 170, 160, 150, 140, 130, 140, 0, 0, 0, 0, 0, 0, 0, 0,
  180, 170, 155, 140, 140, 125, 140, 150, 0, 0, 0, 0, 0, 0, 0, 0,
  170, 160, 140, 120, 110, 140, 150, 160, 0, 0, 0, 0, 0, 0, 0, 0,
  160, 150, 140, 110, 120, 140, 160, 170, 0, 0, 0, 0, 0, 0, 0, 0,
  150, 140, 125, 140, 140, 155, 170, 180, 0, 0, 0, 0, 0, 0, 0, 0,
  140, 130, 140, 150, 160, 170, 180, 190, 0, 0, 0, 0, 0, 0, 0, 0,
  130, 140, 150, 160, 170, 180, 190, 200, 0, 0, 0, 0, 0, 0, 0, 0
};

int kbnk_eval(const position_t *pos) {
  int winner, loser;
  int wksq, bksq, bsq, nsq, sign;
 
  winner = pos->material[WHITE]? WHITE : BLACK;
  loser = winner^1;
  sign = (winner == pos->side)? 1 : -1;
 
  wksq = KingSquare(pos, winner); bksq = KingSquare(pos, loser);
  bsq = BishopListStart(pos, winner); nsq = KnightListStart(pos, winner);

  if((file(bsq) + rank(bsq)) % 2) {
    wksq ^= 7; bksq ^= 7; bsq ^= 7; nsq ^= 7;
  }
 
  return sign*(KNOWN_WIN + DistanceBonus[Distance[wksq-bksq]] +
               KBNKtable[bksq]);
}


Tord

[Steve Maughan]

And how deep does the search have to be to find these mates, with such an evaluation?

Not too much. Monarch is able to mate with B+N at 1 min / game + 1 sec / move against tablebase defence.

Regards,

Steve