CHANGING AND UNCHANGING OF THE RADIUS OF A GRAPH

Harary introduced the concept of changing and unchanging of a graphica l invariant i, asking for characterizations of graphs G = (V, E) for w hich i(G - v), i(G - e) or i(G + e) either differ from i(G) or are equ al to i(G) for all v is an element of V, e is an element of E, or e is an element of (E) over bar, respectively, where (E) over bar is the s et of edges in the complement of G. This paper examines changing and u nchanging properties of the radius of a graph, an important parameter in network design.