TOPICS

# Bouwer Graph

Bouwer graphs, a term coined here for the first time, are a family of regular graphs which includes members that are symmetric but not arc-transitive. Such graphs are termed 1/2-transitive by Alspach et al. (1994).

Bouwer's general construction of such graphs defines a graph with and such that . The vertex set of this graph is identified with the Cartesian product

where denotes the ring of integers modulo , and the edge set consists of pairs of -tuples

for , ..., (with addition mod ) and , ..., such that either for all , 3, ..., , or else there is exactly one for which , in which case it is taken as (mod ).

Such graphs are symmetric by construction, and include the following named graphs which are arc-transitive.

However, this class of graphs also includes members that are symmetric not not edge-transitive. Such graphs were first considered by Tutte (1966), who did not construct any, but showed that if it existed, any such graph must be regular of even degree. The first examples were therefore given by Bouwer (1970), who showed is a connected -regular symmetric arc-intransitive graph for all integers . This class of graphs has vertices, giving graphs with vertex counts 54, 486, 4374, 39366, 354294, ... for , 3, ....

This smallest example of such a graph is the quartic symmetric graph on 54 vertices illustrated above in several embeddings. This graph can be concisely described and constructed from the vertex set , where is joined to , , and (Holt 1981).

Dolye (1976) and Holt (1981) subsequently discovered the smaller symmetric arc-intransitive graph now known as the Doyle graph, which can be obtained from Bouwer's 54-vertex graph by contracting pairs of diametrically opposed vertices (Doyle 1998).

A partial tabulation of small symmetric arc-intransitive graphs constructed using Brouwer's method is given in the following table (Weisstein, Nov. 17, 2010), where is the vertex count. These graphs will are implemented in the Wolfram Language as GraphData["Bouwer", N, m, n].

 54 60 63 84 100

Arc-Transitive Graph, Doyle Graph, Symmetric Graph

## Explore with Wolfram|Alpha

More things to try:

## References

Alspach, B.; Marušič, Dragan; and Nowitz, L. (1994), "Constructing Graphs which are 1/2-Transitive." J. Austral. Math. Soc. 56, 391-402, 1994.Bouwer, I. Z. "Vertex and Edge Transitive, But Not 1-Transitive Graphs." Canad. Math. Bull. 13, 231-237, 1970.Doyle, P. G. On Transitive Graphs. Senior Thesis. Cambridge, MA, Harvard College, April 1976.Doyle, P. "A 27-Vertex Graph That Is Vertex-Transitive and Edge-Transitive But Not L-Transitive." October 1998. http://arxiv.org/abs/math/0703861.Holt, D. F. "A Graph Which Is Edge Transitive But Not Arc Transitive." J. Graph Th. 5, 201-204, 1981.Tutte, W. T. Connectivity in Graphs. Toronto, CA: University of Toronto Press, 1966.

Bouwer Graph

## Cite this as:

Weisstein, Eric W. "Bouwer Graph." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/BouwerGraph.html