Mapping a graph onto itself without changing edge-vertex connectivity
In the mathematical field of graph theory, an automorphism of a graph is a form of symmetry in which the graph is mapped onto itself while preserving the edge–vertex connectivity.
Formally, an automorphism of a graph G = (V, E) is a permutation σ of the vertex set V, such that the pair of vertices (u, v) form an edge if and only if the pair (σ(u), σ(v)) also form an edge. That is, it is a graph isomorphism from G to itself. Automorphisms may be defined in this way both for directed graphs and for undirected graphs.
The composition of two automorphisms is another automorphism, and the set of automorphisms of a given graph, under the composition operation, forms a group, the automorphism group of the graph. In the opposite direction, by Frucht's theorem, all groups can be represented as the automorphism group of a connected graph – indeed, of a cubic graph.[1][2]
^Frucht, R. (1938), "Herstellung von Graphen mit vorgegebener abstrakter Gruppe", Compositio Mathematica (in German), 6: 239–250, ISSN 0010-437X, Zbl 0020.07804.
^Frucht, R. (1949), "Graphs of degree three with a given abstract group" (PDF), Canadian Journal of Mathematics, 1 (4): 365–378, doi:10.4153/CJM-1949-033-6, ISSN 0008-414X, MR 0032987, S2CID 124723321, archived from the original on Jun 9, 2012.
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