High Quality Content by WIKIPEDIA articles! In graph-theoretic mathematics, a voltage graph is a directed graph whose edges are labelled invertibly by elements of a group. It is formally identical to a gain graph, but it is generally used in topological graph theory as a concise way to specify another graph called the derived graph of the voltage graph.Typical choices of the groups used for voltage graphs include the two-element group mathbb{Z}_2 (for defining the bipartite double cover of a graph), free groups (for defining the universal cover of a graph), d-dimensional integer lattices mathbb{Z}^d (viewed as a group under vector addition, for defining periodic structures in d-dimensional Euclidean space), and finite cyclic groups mathbb{Z}_{n} for n > 2. When ? is a cyclic group, the voltage graph may be called a cyclic-voltage graph.

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