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pl:prolog:pllib:minimax_principle [2019/06/27 15:50] (aktualna) |
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| + | ====== Minimax principle ====== | ||
| + | {{tag>problem_solving}} | ||
| + | ===== Description ===== | ||
| + | A straightforward implementation of the minimax principle. | ||
| + | |||
| + | **Source**: PROLOG programming for artificial intelligence, 3rd Edition, Harlow, 2001, ISBN 0-201-40375-7. | ||
| + | ===== Download ===== | ||
| + | Program source code: {{minimax_principle.pl}} | ||
| + | ===== Listing ===== | ||
| + | <code prolog> | ||
| + | % Figure 22.3 A straightforward implementation of the minimax principle. | ||
| + | |||
| + | |||
| + | % minimax( Pos, BestSucc, Val): | ||
| + | % Pos is a position, Val is its minimax value; | ||
| + | % best move from Pos leads to position BestSucc | ||
| + | |||
| + | minimax( Pos, BestSucc, Val) :- | ||
| + | moves( Pos, PosList), !, % Legal moves in Pos produce PosList | ||
| + | best( PosList, BestSucc, Val) | ||
| + | ; | ||
| + | staticval( Pos, Val). % Pos has no successors: evaluate statically | ||
| + | |||
| + | best( [ Pos], Pos, Val) :- | ||
| + | minimax( Pos, _, Val), !. | ||
| + | |||
| + | best( [Pos1 | PosList], BestPos, BestVal) :- | ||
| + | minimax( Pos1, _, Val1), | ||
| + | best( PosList, Pos2, Val2), | ||
| + | betterof( Pos1, Val1, Pos2, Val2, BestPos, BestVal). | ||
| + | |||
| + | betterof( Pos0, Val0, Pos1, Val1, Pos0, Val0) :- % Pos0 better than Pos1 | ||
| + | min_to_move( Pos0), % MIN to move in Pos0 | ||
| + | Val0 > Val1, ! % MAX prefers the greater value | ||
| + | ; | ||
| + | max_to_move( Pos0), % MAX to move in Pos0 | ||
| + | Val0 < Val1, !. % MIN prefers the lesser value | ||
| + | |||
| + | betterof( Pos0, Val0, Pos1, Val1, Pos1, Val1). % Otherwise Pos1 better than Pos0 | ||
| + | </code> | ||
| + | ===== Comments ===== | ||
