[HTML][HTML] On the chromaticity of complete multipartite graphs with certain edges added

GC Lau, YH Peng - Discrete mathematics, 2009 - Elsevier
GC Lau, YH Peng
Discrete mathematics, 2009Elsevier
Let P (G, λ) be the chromatic polynomial of a graph G. A graph G is chromatically unique if
for any graph H, P (H, λ)= P (G, λ) implies H is isomorphic to G. For integers k≥ 0, t≥ 2,
denote by K ((t− 1)× p, p+ k) the complete t-partite graph that has t− 1 partite sets of size p
and one partite set of size p+ k. Let K (s, t, p, k) be the set of graphs obtained from K ((t− 1)×
p, p+ k) by adding a set S of s edges to the partite set of size p+ k such that〈 S〉 is bipartite.
If s= 1, denote the only graph in K (s, t, p, k) by K+ ((t− 1)× p, p+ k). In this paper, we shall …
Let P(G,λ) be the chromatic polynomial of a graph G. A graph G is chromatically unique if for any graph H, P(H,λ)=P(G,λ) implies H is isomorphic to G. For integers k≥0, t≥2, denote by K((t−1)×p,p+k) the complete t-partite graph that has t−1 partite sets of size p and one partite set of size p+k. Let K(s,t,p,k) be the set of graphs obtained from K((t−1)×p,p+k) by adding a set S of s edges to the partite set of size p+k such that 〈S〉 is bipartite. If s=1, denote the only graph in K(s,t,p,k) by K+((t−1)×p,p+k). In this paper, we shall prove that for k=0,1 and p+k≥s+2, each graph G∈K(s,t,p,k) is chromatically unique if and only if 〈S〉 is a chromatically unique graph that has no cut-vertex. As a direct consequence, the graph K+((t−1)×p,p+k) is chromatically unique for k=0,1 and p+k≥3.
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