Minimal configuration unicyclic graphs.

A graph G is singular with nullity η(G), if zero is an eigenvalue of its adjacency matrix with multiplicity η(G). If η(G) = 1, then the core of G is the subgraph induced by the vertices associated with the non-zero entries of the kernel eigenvector. The set of vertices which are not in the core is called the periphery of G. A graph G with nullity one is called a minimal configuration if no two vertices in the periphery are adjacent and deletion of any vertex in the periphery increases the nullity. In this article, we describe the structure of a singular unicyclic graph and single out the class of unicyclic graphs which are minimal configurations. [ABSTRACT FROM AUTHOR]