Cospectral graphs and digraphs with given automorphism group

THE AUTOMORPHISM GROUP OF FINITE GRAPHS

Let G = (V,E) be a simple graph with exactly n vertices and m edges. The aim of this paper is a new method for investigating nontriviality of the automorphism group of graphs. To do this, we prove that if |E| >=[(n - 1)2/2] then |Aut(G)|>1 and |Aut(G)| is even number.

Vector representable matroids of given rank with given automorphism group

A simple way of as,;ociating a matroid of prescribed rank with a graph is shown. The matroids so corhstrueted are re.presentable over any sufficiently large field. Their ase is demonstrated by the fallowing result: Given an integer k >~ 3 and a hmction G associating a group with each subsel of a set S, the'e is a matroid M(E), representable ever any sufl]ciendy large field, such that E ~S, and ...

Graphs with given Group

Subdirectly Reducible Groups and Edge-minimal Graphs with given Automorphism Group

A group is subdirectly reducible if it has two non-trivial normal subgroups with trivial intersection. Such groups may be an easy case in certain inductive arguments. We prove that every solvable finite group can be generated by at most one subdirectly reducible subgroup together with two subgroups of prime-power order and one element. We also prove that every group of prime-power order can be ...

Graphs cospectral with starlike trees

A tree which has exactly one vertex of degree greater than two is said to be starlike. In spite of seemingly simple structure of these trees, not much is known about their spectral properties. In this paper, we introduce a generalization of the notion of cospectrality called m-cospectrality which turns out to be useful in constructing cospectral graphs. Based on this, we construct cospectral ma...