本節では評価パラメータを更新する関数Evaluator_Update()について説明します。

• 各パターンの更新

  まず各パターンの評価値を更新する関数Evaluator_UpdatePattern()を見てみましょう。
  

  static void Evaluator_UpdatePattern(Evaluator *self, int in_pattern, int in_id, int in_mirror, int in_diff)
  {
  	if (MAX_PATTERN_VALUE - in_diff < self->Value[in_pattern][in_id]) {
  		self->Value[in_pattern][in_id] = MAX_PATTERN_VALUE;
  	} else if (-MAX_PATTERN_VALUE - in_diff > self->Value[in_pattern][in_id]) {
  		self->Value[in_pattern][in_id] = -MAX_PATTERN_VALUE;
  	} else {
  		self->Value[in_pattern][in_id] += in_diff;
  	}
  	if (in_mirror >= 0) {
  		self->Value[in_pattern][in_mirror] = self->Value[in_pattern][in_id];
  	}
  }
  

  引数は以下の通りです。
  self : Evaluatorクラスへのポインタ
  in_pattern : 更新を行うパターンの種類
  in_id : 更新を行うパターンインデックス
  in_mirror : 更新を行うパターンと対称なパターンのインデックス
  in_diff : 評価値の差分
  

  in_patternとin_idで決まるパターンの評価値をin_diffだけ増やしています。
  ただしパターンの評価値が-MAX_PATTERN_VALUEからMAX_PATTERN_VALUEまでの間に収まるようにしています。
  また対称なパターンが存在する場合には、そのパターンの評価値も更新します。
  

• 評価値の更新

  それでは評価パラメータを更新する関数Evaluator_Update()の内部を見てみましょう。
  この関数もちょっと長いですが、全部記述します。
  

  void Evaluator_Update(Evaluator *self, const Board *in_board, int in_value)
  {
  	int index, diff;
  
  	diff = (int)((in_value - Evaluator_Value(self, in_board)) * UPDATE_RATIO);
  	index = BOARD_INDEX_8(in_board, A4, B4, C4, D4, E4, F4, G4, H4);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE4, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A5, B5, C5, D5, E5, F5, G5, H5);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE4, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, D1, D2, D3, D4, D5, D6, D7, D8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE4, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, E1, E2, E3, E4, E5, E6, E7, E8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE4, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A3, B3, C3, D3, E3, F3, G3, H3);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE3, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A6, B6, C6, D6, E6, F6, G6, H6);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE3, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, C1, C2, C3, C4, C5, C6, C7, C8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE3, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, F1, F2, F3, F4, F5, F6, F7, F8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE3, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A2, B2, C2, D2, E2, F2, G2, H2);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE2, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A7, B7, C7, D7, E7, F7, G7, H7);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE2, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, B1, B2, B3, B4, B5, B6, B7, B8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE2, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, G1, G2, G3, G4, G5, G6, G7, G8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_LINE2, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A1, B2, C3, D4, E5, F6, G7, H8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG8, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A8, B7, C6, D5, E4, F3, G2, H1);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG8, self->MirrorLine[index], index, diff);
  	index = BOARD_INDEX_7(in_board, A2, B3, C4, D5, E6, F7, G8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG7, self->MirrorLine[index * POW_3_1], index, diff);
  	index = BOARD_INDEX_7(in_board, B1, C2, D3, E4, F5, G6, H7);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG7, self->MirrorLine[index * POW_3_1], index, diff);
  	index = BOARD_INDEX_7(in_board, A7, B6, C5, D4, E3, F2, G1);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG7, self->MirrorLine[index * POW_3_1], index, diff);
  	index = BOARD_INDEX_7(in_board, B8, C7, D6, E5, F4, G3, H2);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG7, self->MirrorLine[index * POW_3_1], index, diff);
  	index = BOARD_INDEX_6(in_board, A3, B4, C5, D6, E7, F8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG6, self->MirrorLine[index * POW_3_2], index, diff);
  	index = BOARD_INDEX_6(in_board, C1, D2, E3, F4, G5, H6);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG6, self->MirrorLine[index * POW_3_2], index, diff);
  	index = BOARD_INDEX_6(in_board, A6, B5, C4, D3, E2, F1);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG6, self->MirrorLine[index * POW_3_2], index, diff);
  	index = BOARD_INDEX_6(in_board, C8, D7, E6, F5, G4, H3);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG6, self->MirrorLine[index * POW_3_2], index, diff);
  	index = BOARD_INDEX_5(in_board, A4, B5, C6, D7, E8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG5, self->MirrorLine[index * POW_3_3], index, diff);
  	index = BOARD_INDEX_5(in_board, D1, E2, F3, G4, H5);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG5, self->MirrorLine[index * POW_3_3], index, diff);
  	index = BOARD_INDEX_5(in_board, A5, B4, C3, D2, E1);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG5, self->MirrorLine[index * POW_3_3], index, diff);
  	index = BOARD_INDEX_5(in_board, D8, E7, F6, G5, H4);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG5, self->MirrorLine[index * POW_3_3], index, diff);
  	index = BOARD_INDEX_4(in_board, A5, B6, C7, D8);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG4, self->MirrorLine[index * POW_3_4], index, diff);
  	index = BOARD_INDEX_4(in_board, E1, F2, G3, H4);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG4, self->MirrorLine[index * POW_3_4], index, diff);
  	index = BOARD_INDEX_4(in_board, A4, B3, C2, D1);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG4, self->MirrorLine[index * POW_3_4], index, diff);
  	index = BOARD_INDEX_4(in_board, E8, F7, G6, H5);
  	Evaluator_UpdatePattern(self, PATTERN_ID_DIAG4, self->MirrorLine[index * POW_3_4], index, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, A1, B1, C1, D1, E1, F1, G1, B2), -1, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, H1, G1, F1, E1, D1, C1, B1, G2), -1, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, A8, B8, C8, D8, E8, F8, G8, B7), -1, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, H8, G8, F8, E8, D8, C8, B8, G7), -1, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, A1, A2, A3, A4, A5, A6, A7, B2), -1, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, A8, A7, A6, A5, A4, A3, A2, B7), -1, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, H1, H2, H3, H4, H5, H6, H7, G2), -1, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_EDGE8, BOARD_INDEX_8(in_board, H8, H7, H6, H5, H4, H3, H2, G7), -1, diff);
  	index = BOARD_INDEX_8(in_board, A1, B1, C1, A2, B2, C2, A3, B3);
  	Evaluator_UpdatePattern(self, PATTERN_ID_CORNER8, self->MirrorCorner[index], index, diff);
  	index = BOARD_INDEX_8(in_board, H1, G1, F1, H2, G2, F2, H3, G3);
  	Evaluator_UpdatePattern(self, PATTERN_ID_CORNER8, self->MirrorCorner[index], index, diff);
  	index = BOARD_INDEX_8(in_board, A8, B8, C8, A7, B7, C7, A6, B6);
  	Evaluator_UpdatePattern(self, PATTERN_ID_CORNER8, self->MirrorCorner[index], index, diff);
  	index = BOARD_INDEX_8(in_board, H8, G8, F8, H7, G7, F7, H6, G6);
  	Evaluator_UpdatePattern(self, PATTERN_ID_CORNER8, self->MirrorCorner[index], index, diff);
  	Evaluator_UpdatePattern(self, PATTERN_ID_PARITY, Board_CountDisks(in_board, EMPTY) & 1, -1, diff);
  }
  

  この関数も、処理の内容は単純です。
  まず最初に以下の式によって評価値の差分を決めています。
  

  （（与えられた局面評価値）−（Evaluatorによる局面評価値）） X （更新の度合い）

  次に局面に含まれるパターンを抽出し、各パターンの評価値更新を行っています。
  こうすると、Evaluatorによって得られる評価値が、与えられた局面評価値にだんだん近づくようになります。
  

  式にある更新の度合いは、評価値をどの程度増減するかを決める値です。
  小さすぎるとなかなか評価パラメータが更新されず、適切な値になりません。
  かといって大きすぎると評価パラメータが安定しません。
  ここでは0.003を使用することにしました。
  必ずしも最適な値というわけではありませんが、ある程度適切な評価パラメータが得られることを確認しています。