For any h ∈ N, a graph G = (V, E) is said to be h-magic if there exists a labeling l : E(G) → Zh−{0} such that the induced vertex labeling l+ : V (G) → Zh defined by l(v) = ∑ uv∈E(G) l(uv) is a constant map. When this constant is 0 we call G a zero-sum h-magic graph. The null set of G is the set of all natural numbers h ∈ N for which G admits a zero-sum h-magic labeling. A graph G is said to be...

Given a graph G = (V, E), with each subset X of V is associated the subgraph G(X) of G induced by X. A subset I of V is an interval of G provided that for any a, b ∈ I and x ∈ V \ I , {a, x} ∈ E if and only if {b, x} ∈ E. For example, ∅, {x}, where x ∈ V , and V are intervals of G called trivial intervals. A graph is indecomposable if all its intervals are trivial; otherwise, it is decomposable...

For any h ∈ IN , a graph G = (V, E) is said to be h-magic if there exists a labeling l : E(G) −→ ZZ h − {0} such that the induced vertex set labeling l : V (G) −→ ZZ h defined by l(v) = ∑ uv∈E(G) l(uv) is a constant map. For a given graph G, the set of all h ∈ ZZ + for which G is h-magic is called the integer-magic spectrum of G and is denoted by IM(G). The concept of integer-magic spectrum of ...

Su, X.-Y., A result on decompositions of regular graphs, Discrete Mathematics 105 (1992) 323-326. We prove that for any connected graph G and any integer r which is a common multiple of the degrees of the vertices in G, there exists a connected, r-regular, and G-decomposable graph H such that x(H) = x(G) and o(H) = w(G), where x and w are the chromatic number and the clique number, respectively...

An additive hereditary graph property is a class of simple graphs which is closed under unions, subgraphs and isomorphisms. If P1, . . . ,Pn are graph properties, then a (P1, . . . ,Pn)-decomposition of a graph G is a partition E1, . . . , En of E(G) such that G[Ei], the subgraph of G induced by Ei, is in Pi, for i = 1, . . . , n. The sum of the properties P1, . . . ,Pn is the property P1 ⊕ · ·...

A graph G = (V, E) is said to be magic if there exists an integer labeling f : V ∪ E −→ [1, |V ∪ E|] such that f(x) + f(y) + f(xy) is constant for all edges xy ∈ E. Enomoto, Masuda and Nakamigawa proved that there are magic graphs of order at most 3n + o(n) which contain a complete graph of order n. Bounds on Sidon sets show that the order of such a graph is at least n + o(n). We close the gap ...

Let G = (V,E) be a graph of order n. A bijection f : V → {1, 2, . . . , n} is called a distance magic labeling of G if there exists a positive integer k such that ∑ u∈N(v) f(u) = k for all v ∈ V, where N(v) is the open neighborhood of v. The constant k is called the magic constant of the labeling f . Any graph which admits a distance magic labeling is called a distance magic graph. In this pape...

Let M = (V, E, A) be a mixed graph with vertex set V , edge set E and arc set A. A cycle cover of M is a family C = {C1, . . . ,Ck} of cycles of M such that each edge/arc of M belongs to at least one cycle in C. The weight of C is ∑k i=1 |Ci |. The minimum cycle cover problem is the following: given a strongly connected mixed graph M without bridges, find a cycle cover of M with weight as small...

In this paper, a generalization of a group-magic graph is introduced and studied. Let R be a commutative ring with unity 1. A graph G = (V,E) is called R-ring-magic if there exists a labeling f : E → R−{0} such that the induced vertex labelings f : V → R, defined by f(v) = Σf(u, v) where (u, v) ∈ E, and f : V → R, defined by f(v) = Πf(u, v) where (u, v) ∈ E, are constant maps. General algebraic...

For any k ∈ N, a graph G = (V,E) is said to be Zk-magic if there exists a labeling l : E(G) −→ Zk − {0} such that the induced vertex set labeling l : V (G) −→ Zk defined by l(v) = ∑ u∈N(v) l(uv) is a constant map. For a given graph G, the set of all k ∈ Z+ for which G is Zk-magic is called the integer-magic spectrum of G and is denoted by IM(G). In this paper we will consider trees whose diamet...