Convex labelings of trees

Abstract

AbstractA convex labeling of a tree T of order n is a one‐to‐one function f from the vertex set of T into the nonnegative integers, so that f(y) ⩽ (f(x) + f(z))/2 for every path x, y, z of length 2 in T. If, in addition, f(v) ⩽ n − 1 for every vertex v of T, then f is a perfect convex labeling and T is called a perfectly convex tree. Jamison introduced this concept and conjectured that every tree is perfectly convex. We show that there exists an infinite class of trees, none of which is perfectly convex, and in fact prove that for every n there exists a tree of order n which requires a convex labeling with maximum value at least 6n/5 – 22. We also prove that every tree of order n admits a convex labeling with maximum label no more than n2/8 + 2. In addition, we present some constructive methods for obtaining perfect convex labelings of large classes of trees.