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A note on large graphs of diameter two and given maximum degree. (English) Zbl 0911.05031
The well-known degree/diameter problem asks for determining the largest number of vertices in a graph of maximum degree $$d$$ and diameter $$k$$. In this paper the case of vertex-transitive graphs and $$k=2$$ is considered. The upper (Moore) bound is $$d^2+1$$, but the previously known lower bound was asymptotically only $$d^2/4$$. Using voltage graphs, the authors construct vertex-transitive non-Cayley graphs with asymptotically $$8d^2/9$$ vertices for a selected sequence of $$d$$’s.

##### MSC:
 05C12 Distance in graphs 05C35 Extremal problems in graph theory 05C25 Graphs and abstract algebra (groups, rings, fields, etc.)
##### Keywords:
graph; degree; diameter; group; Moore bound; vertex-transitive
nauty
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##### References:
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