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An admissible heuristic is used to estimate the cost of reaching the goal state in an informed search algorithm. In order for a heuristic to be admissible to the search problem, the estimated cost must always be lower than or equal to the actual cost of reaching the goal state. The search algorithm uses the admissible heuristic to find an ...
In such search problems, a heuristic can be used to try good choices first so that bad paths can be eliminated early (see alpha–beta pruning). In the case of best-first search algorithms, such as A* search, the heuristic improves the algorithm's convergence while maintaining its correctness as long as the heuristic is admissible.
The algorithm continues until a removed node (thus the node with the lowest f value out of all fringe nodes) is a goal node. [b] The f value of that goal is then also the cost of the shortest path, since h at the goal is zero in an admissible heuristic. The algorithm described so far only gives the length of the shortest path.
Like A*, LPA* uses a heuristic, which is a lower boundary for the cost of the path from a given node to the goal. A heuristic is admissible if it is guaranteed to be non-negative (zero being admissible) and never greater than the cost of the cheapest path to the goal.
Comparison of an admissible but inconsistent and a consistent heuristic evaluation function. Consistent heuristics are called monotone because the estimated final cost of a partial solution, () = + is monotonically non-decreasing along any path, where () = = (,) is the cost of the best path from start node to .
Heuristic algorithms (1 C, 16 P) R. Razors ... (15 P) Rules of thumb (2 C, 63 P) Pages in category "Heuristics" ... Admissible heuristic; Affect heuristic; Anchoring ...
Iterative deepening A* (IDA*) is a graph traversal and path search algorithm that can find the shortest path between a designated start node and any member of a set of goal nodes in a weighted graph. It is a variant of iterative deepening depth-first search that borrows the idea to use a heuristic function to conservatively estimate the ...
The BHFFA algorithm of de Champeaux fixed this defect. [3] A solution found by the uni-directional A* algorithm using an admissible heuristic has a shortest path length; the same property holds for the BHFFA2 bidirectional heuristic version described by de Champeaux . [4] BHFFA2 has, among others, more careful termination conditions than BHFFA.