Some Algebraic Properties of Bi-Cayley Graphs Hua Zou and Jixiang Meng College of Mathematics and Systems Science,Xinjiang University

Circulant Graph When G is a cyclic group, the Cayley digraph(graph) D(G;S)(C(G;S)) is called a circulant digraph(graph). Cayley Graph For a group G and a subset S of G, the Cayley digraph D(G; S) is a graph with vertex set G and arc set. When,D(G,S) corresponds to an undirected graph C(G,S), which is called a Cayley graph. 1.Definition

Bi-Cayley Graph For a finite group G and a subset T of G, the Bi-Cayley graph X=BC(G,T) is defined as the bipartite graph with vertex set and edge set

Example:

Theorem2.2. Let G be an abelian group and let be the eigenvalues of the Cayley digraph D(G,S). Then the eigenvalues of BC(G,S) are Theorem 2.1. The adjacency matrix of a Cayley digraph of abelian group is normal. We use T(G,S) to denote the number of spanning trees of a Connected Bi-Circulant graph BC(G,S). 2.Main Result

Since the eigenvalues of an undirected graph are real, we deduce the following corollary by Theorem 2.2. Corollary 2.3. Let be the eigenvalues of C(G,S). Then the eigenvalues of BC(G,S) are

Theorem2.4. Let G be a cyclic group of integers modulo n and be a subset of G. (2)If S=-S, the eigenvalues of the Bi-Circulant graph BC(G,S) are (1)The eigenvalues of the Bi-Circulant digraph BC(G,S) are

Theorem2.5. Let G be a cyclic group of integers modulo n and S be a subset of G.If S is a union of some, then BC(G,S) is integral. In particular, if S=-S, then BC(G,S) is integral if and only if S is a union of some

Lemma 2.6. Let G be a cyclic group of integers modulo n. Let be a subset of G with S=-S. If the polynomial have the roots,then where

Lemma 2.7. Let where If, then the roots of f(z) satisfy

Theorem 2.8. Let BC(G,S) be the connected Bi-Circulant graph of order n. Then

Theorem 2.9.Let BC(G,S) be the connected Bi-irculant graph of order n.Then

3.Recent Main Result For a digraph D with, we define Example:

Theorem 3.1 Let D be a digraph and A be its adjacency matrix. Let be the eigenvalues of A. If A is normal,the eigenvalues of the adjacency matrix of are For a graph X with,we define graph of X where is the associated digraph of X.

Corollary 3.2 Let D be a graph. Let be the eigenvalues of the adjacency matrix of D.Then the eigenvalues of are

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