Strongly connected graph
In the mathematical theory of directed graphs, a graph is said to be strongly connected if every vertex is strongly connected components of an arbitrary directed graph form a partition into subgraphs that are themselves stro ngly connected. It is possible to test the strong connectivity of a graph, or to fi n d its time.
Definitions
A directed graph is called strongly direction between each pair of vertices of the graph. In a directed graph G that may not itself be strongly connected, a pair of vertices u and v are said to be strongly connected to each other if there is a path in each direction between them.
connected is an equivalence relation, and the induced subgraphs of its equivalence strongly connected component of a directed graph G is a subgraph that is strongly connected, and is maximal with this prop erty: no additional edges or vertices from G can be included in the subgraph without for ms a partition of the set of vertices of G.I f each strongly connected component is contracted to a single vertex, the resulting graph is a directed acyclic graph, the condensation of G. A directed graph is acyclic if and only if it has no connected and every nontrivial strongly connected component contains at least one directed cycle.
Algorithms
href="http://en.wikipedia.org/wiki/Linear_time">linear time.- Kosaraju's algorithm uses two passes of transpose graph of the original graph, and each recursive exploration finds a single new strongly connected described it (but did not publish his results) in 1978; Micha Sharir later published it in 1981.
- Tarjan's strongly connected components
1972, performs a single pass of depth first search. It maintains a
- The path-based strong component algorithm uses a to keep track of the vertices not yet assigned to components, while the other kee p s track of the published by Edsger W. Dijkstra in 1976.
Although Kosaraju's algorithm is conceptually simple, Tarjan's and the path-based algorithm are favoured in practice since they require only o
Applications
Algorithm s for finding strongly connected components may be used to variables wi th constraints on the values of pairs of variables): as showed, a 2-satisfiability instance is unsatisfiable if and only if there is a variable v such that v and its complement are both c ontained in
Strongly connected components are also used to compute the Dulmage–Mendelsohn decomposition, a of the edges of a bipartite graph, according to whether or not they can be part of a perfect matching
Related results
A directed graph is strongly connected if and only if it has an ear decomposition, a partition of the edges into a sequence of directed paths and cycles such that the first subgraph in the sequence is a cycle, and each subsequent subgraph is either a cycle sharing one vertex with previous subgraphs, or a path
According to Robbins' theorem, an undirected graph
may be oriented in such a way that it becomes
strongly connected, if and only if it is
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