Equivalently, a forest is an undirected acyclic graph. CRFs are a type of discriminative undirected probabilistic graphical model. Thus, symmetric relations and undirected graphs are combinatorially equivalent objects. The original algorithm is applicable to undirected, weighted and unweighted graphs. Local connectivity is symmetric for undirected graphs; that is, . Similar to undirected graphs, DOT can describe directed graphs, such as flowcharts and dependency trees. The corresponding concept for undirected graphs is a forest, an undirected graph without cycles. An undirected graph that is not connected is called disconnected. Similar ideas may be applied to undirected, and possibly cyclic, graphs such as Markov networks. The shortest path problem can be defined for graphs whether undirected, directed, or mixed. A tree is a connected undirected graph with no cycles. The connected components of an undirected graph can be identified in linear time. Directed and undirected graphs are special cases. They also present a faster algorithm that takes formula 77 rounds in undirected graphs. Here is a simple example of a labelled, undirected graph and its Laplacian matrix.