The total monophonic number of a graph

K. Ganesamoorthy1, M. Murugan1, A.P. Santhakumaran2, P. Titus3
1Department of Mathematics, Coimbatore Institute of Technology, Coimbatore – 641 014, India
2Department of Mathematics, Hindustan Institute of Technology and Science, Chennai – 603 103, India
3Department of Mathematics, University College of Engineering Nagercoil, Anna University, Tirunelveli Region, Nagercoil – 629 004, India

Abstract

For a connected graph G of order at least two, a total monophonic set of a graph G is a monophonic set S such that the subgraph G[S] induced by S has no isolated vertices. The minimum cardinality of a total monophonic set of G is the total monophonic number of G and is denoted by mt(G). We determine bounds for it and characterize graphs which realize the lower bound. Also, some general properties satisfied by this concept are studied. It is shown that for positive integers a, b such that 3 ≤ a ≤ b with b ≤ 2a, there exists a connected graph G such that m(G) = a and mt(G) = b. Further, if p, a, b are positive integers such that 4 ≤ a ≤ b ≤ p, then there exists a connected graph G of order p with mt(G) = a and mc(G) = b, where mc(G) is the connected monophonic number of G.

Keywords: monophonic set, monophonic number, total monophonic set, total monophonic number