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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Bidirectional search ： ウィキペディア英語版 Bidirectional search Bidirectional search is a graph search algorithm that finds a shortest path from an initial vertex to a goal vertex in a directed graph. It runs two simultaneous searches: one forward from the initial state, and one backward from the goal, stopping when the two meet in the middle. The reason for this approach is that in many cases it is faster: for instance, in a simplified model of search problem complexity in which both searches expand a tree with branching factor ''b'', and the distance from start to goal is ''d'', each of the two searches has complexity ''O''(''b''''d''/2) (in Big O notation), and the sum of these two search times is much less than the ''O''(''b''''d'') complexity that would result from a single search from the beginning to the goal. As in A * search, bi-directional search can be guided by a heuristic estimate of the remaining distance to the goal (in the forward tree) or from the start (in the backward tree). was the first one to design and implement a bi-directional heuristic search algorithm. Andrew Goldberg and others explained the correct termination conditions for the bidirectional version of Dijkstra’s Algorithm.〔(Efficient Point-to-Point Shortest Path Algorithms )〕 == Description == A Bidirectional Heuristic Search is a state space search from some state $s$ to another state $t$, searching from $s$ to $t$ and from $t$ to $s$ simultaneously. It returns a valid list of operators that if applied to $s$ will give us $t$. While it may seem as though the operators have to be invertible for the reverse search, it is only necessary to be able to find, given any node $n$, the set of parent nodes of $n$ such that there exists some valid operator from each of the parent nodes to $n$. This has often been likened to a one-way street in the route-finding domain: it is not necessary to be able to travel down both directions, but it is necessary when standing at the end of the street to determine the beginning of the street as a possible route. Similarly, for those edges that have inverse arcs (i.e. arcs going in both directions) it is not necessary that each direction be of equal cost. The reverse search will always use the inverse cost (i.e. the cost of the arc in the forward direction). More formally, if $n$ is a node with parent $p$, then $k\_1(p,n)\; =\; k\_2(n,p)$, defined as being the cost from $p$ to $n$.(Auer Kaindl 2004) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bidirectional search」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.