For any two vertices u and v in a connected graph G, a u − v path is a monophonic path if it contains no chords, and the monophonic distance d m (u, v) is the length of a longest u − v monophonic path in G. For any vertex v in G, the monophonic eccentricity of v is e m (v) = max {d m (u, v) : u ∈ V}. The subgraph induced by the vertices of G having minimum monophonic eccentricity is the monophonic center of G, and it is proved that every graph is the monophonic center of some graph. Also it is proved that the monophonic center of every connected graph G lies in some block of G. With regard to convexity, this monophonic distance is the basis of some detour monophonic parameters such as detour monophonic number, upper detour monophonic number, forcing detour monophonic number, etc. The concept of detour monophonic sets and detour monophonic numbers by fixing a vertex of a graph would be introduced and discussed. Various interesting results based on these parameters are also discussed in this chapter.Keywords: monophonic path, monophonic distance, detour monophonic number, upper detour monophonic number, forcing detour monophonic number, vertex detour monophonic number, upper vertex detour monophonic number, forcing vertex detour monophonic number Graph Theory -Advanced Algorithms and Applications 116The following result is an easy consequence of the respective definitions.
Proposition 2.3. Let u and v be any two vertices in a graph G of order p. ThenResult 2.4. Let u and v be any two vertices in a connected graph G. Then (i) d m (u, v) = 0 if and only if u = v. (ii) d m (u, v) = 1 if and only if uv is an edge of G. (iii) d m (u, v) = p − 1 if and only if G is the path with endvertices u and v.(iv) d(u, v) = d m (u, v) = D(u, v) if and only if G is a tree. Definition 2.5. For any vertex v in a connected graph G, the monophonic eccentricity of v is e m (v) = max {d m (u, v) : u ∈ V}. A vertex u of G such that d m (u, v) = e m (v) is called a monophonic eccentric vertex of v. The monophonic radius and monophonic diameter of G are defined by rad m G = min {e m (v) : v ∈ V} and diam m G = max {e m (v) : v ∈ V}, respectively.Example 2.6. Table 1 shows the monophonic distance between the vertices and also the monophonic eccentricities of vertices of the graph G given in Figure 1. It is to be noted that rad m G = 3 and diam m G = 5.Remark 2.7. In any connected graph, the eccentricity of every two adjacent vertices differs by at most 1. However, this is not true in the case of monophonic distance. For the graph G given in Figure 1, e m (v 5 ) = 3 and e m (v 6 ) = 5. Note 2.8. Any two vertices u and v in a tree T are connected by a unique path, and so d(u, v) = d m (u, v) = D(u, v). Hence rad T = rad m T = rad D T and diam T = diam m T = diam D T.The monophonic radius and the monophonic diameter of some standard graphs are given in Table 2. Figure 1. The graph G in Example 2.2.Monophonic Distance in Graphs http://dx.doi.org/10.5772/intechopen.68668 117Graph Theory -Advanced Algorithms and Applications 132