In this paper, we extend the idea of magic labeling to directed graphs. In particular, a magic labeling of a digraph is the directed analog of a vertex-magic total labeling. Some elementary results are obtained and some infinite families of magic digraph labelings are exhibited.

Let \( P_h \) be a path on \( h \) vertices. A simple graph \( G = (V, E) \) admits a \( P_h \)-covering if every edge in \( E \) belongs to a subgraph of \( G \) that is isomorphic to \( P_h \). \( G \) is called \( P_h \)-magic if there is a total labeling \( f: V \cup E \to \{1, 2, \dots, |V| + |E|\} \) such that for each subgraph \( H’ = (V’, E’) \) of \( G \) that is isomorphic to \( P_h \), \( \sum_{v \in V’} f(v) + \sum_{e \in E’} f(e) \) is constant. When \( f(V) = \{1, 2, \dots, |V|\} \), we say that \( G \) is \( P_h \)-supermagic.

In this paper, we study some \( P_h \)-supermagic trees. We give some sufficient or necessary conditions for a tree to be \( P_h \)-supermagic. We also consider the \( P_h \)-supermagicness of special types of trees, namely shrubs and banana trees.

A \((p, q)\)-graph \( G \) is said to be multiplicative if its vertices can be assigned distinct positive integers so that the values of the edges, obtained as the products of the numbers assigned to their end vertices, are all distinct. Such an assignment is called a multiplicative labeling of \( G \). A multiplicative labeling is said to be \((a, r)\)-geometric if the values of the edges can be arranged as a geometric progression \( a, ar, ar^2, \dots, ar^{q-1} \). In this paper, we prove that some well-known classes of graphs are geometric for certain values of \( a, r \) and also initiate a study on the structure of finite \((a, r)\)-geometric graphs.

Given an integer \( \lambda \geq 2 \), a graph \( G = (V, E) \) and a spanning subgraph \( H \) of \( G \) (the backbone of \( G \)), a \( \lambda \)-backbone coloring of \( (G, H) \) is a proper vertex coloring \( V \to \{1, 2, \dots\} \) of \( G \), in which the colors assigned to adjacent vertices in \( H \) differ by at least \( \lambda \). We study the computational complexity of the problem “Given a graph \( G \) with a backbone \( H \), and an integer \( \ell \), is there a \( \lambda \)-backbone coloring of \( (G, H) \) with at most \( \ell \) colors?” Of course, this general problem is NP-complete. In this paper, we consider this problem for collections of pairwise disjoint complete graphs with order \( n \). We show that the complexity jumps from polynomially solvable to NP-complete between \( \ell = (n – 1)\lambda \) and \( \ell = (n – 1)\lambda + 1 \).

For a simple graph \( G = (V(G), E(G)) \) with the vertex set \( V(G) \) and the edge set \( E(G) \), a labeling \( \lambda: V(G) \cup E(G) \to \{1, 2, \dots, k\} \) is called an edge-irregular total \( k \)-labeling of \( G \) if for any two different edges \( e = e_1e_2 \) and \( f = f_1f_2 \) in \( E(G) \) we have \( wt(e) \neq wt(f) \) where \( wt(e) = \lambda(e_1) + \lambda(e) + \lambda(e_2) \). The total edge-irregular strength, denoted by \( tes(G) \), is the smallest positive integer \( k \) for which \( G \) has an edge-irregular total \( k \)-labeling. In this paper, we determine the total edge-irregular strength of the corona product of paths with some graphs.