VoL 43 ,No. 5 Journal of Shanghai Normal University( Natural Sciences · Mathematics)
DOI :10. 3969/J. ISSN. 100 -5137. 2014.05.007
Oct., 2014
The Cayley graph built upon the semigroup of
left ideals of a ring
Ailuia Li1, Ralph P. rFucci2
(I. Department of Mathematical Sciences, Montclair State University, Montclair, New Jersey 07043, USA
;
2. Department of Mathematical Sciences, Loyola University New Orleans, New Orleans, Louisiana 70118, USA)
Abstract: We investigate the interaction between a ring R and the Cayley graph Cay(JL(R) ) of the
semigroup of left ideals of i?,as well as subdigraphs of this graph. Graph theoretic properties of these
graphs are investigated, such as transitive closure, girth, radius, diameter, and spanning subgraphs.
Conditions on certain of these graphs are given which imply that R is regular, left duo, or that the
idempotents of R are central. We characterize simple rings in terms of Cay(IL(/?) ). We characterize
strongly regular rings in terms of a subdigraph of Cay(IL(/?)).
Key words : Cayley graph ; semigroup ; left ideal
€L€ number: 0157.5, 0152.7, 0153.3 Document code: A
Article ID: 1000-5137(2014)05-0506-05
2010 Mathematics Subject Classification. 05C25, 05E99, 20M10.
I Introduction
A directed graph or digraph Gisa pair of sets, the set V of vertices and the set E of edges, denoted G =
(V,E) , where V 7^0 and EQV xV. Ii v ,we.V and (v,w) , then (v yw) is denoted by v —^ w. The edge
v —^ w is said to be incident from v and incident to w. An edge from v to itself is a loop. We allow multiple ed
ges between two vertices of G. Directed graphs with loops and multiple edges are often referred to as quivers. A
subdigraph of G is a digraph Gt - {Vr ,Et) ,where V' QV and Et QE.
A path of length n in G from vertex v to vertex ΐί; is a sequence of edges v v2m'm —^vn —w where
the vertices are all distinct. The distance from i; to ΐί; is the length of the shortest path from v io w. The eccen
tricity of a vertex v is the maximum of its finite distances to all other vertices. The radius of G is the minimum
eccentricity of all its vertices. The diameter of G is the maximum eccentricity of all its vertices; i. e. ,the diam
eter is the maximum distance between all pairs of distinct vertices in G.
A digraph G is strongly connected if there is a path from any vertex to any other vertex. A maximal strong
ly connected subdigraph of G is a strongly connected component of G.
A cycle from vertex v to itself in G is a path from v to some vertex w together with an edge from w to v. The
girth of G is the length of the smallest cycle in G. The circumference of G is the length of the largest cycle
in G.
If G = (V,E) is a directed graph, then the underlying graph of G is the undirected graph Gt - (V \E r ),
Received date
:
2014-07-20
Corresponding author
:
Aihua Li, Professor, E-mail
:
Iia@ mail, montcair. edu
;
Ralph P. Tucci, Professor, E-mail
:
tucci@
loyno. edu