On Grundy total domination number in product graphs

TL;DR

This paper investigates the Grundy total domination number in various standard graph products, establishing bounds, formulas, and conjectures to deepen understanding of this graph invariant.

Contribution

It provides new bounds, formulas, and conjectures for the Grundy total domination number across four standard graph products.

Findings

Established lower bounds for direct and strong products.

Derived explicit formulas for lexicographic product.

Proved bounds for Cartesian product with paths and cycles.

Abstract

A longest sequence $(v_1,\ldots,v_k)$ of vertices of a graph $G$ is a Grundy total dominating sequence of $G$ if for all $i$, $N(v_i) \setminus \bigcup_{j=1}^{i-1}N(v_j)\not=\emptyset$. The length $k$ of the sequence is called the Grundy total domination number of $G$ and denoted $\gamma_{gr}^{t}(G)$. In this paper, the Grundy total domination number is studied on four standard graph products. For the direct product we show that $\gamma_{gr}^t(G\times H) \geq \gamma_{gr}^t(G)\gamma_{gr}^t(H)$, conjecture that the equality always holds, and prove the conjecture in several special cases. For the lexicographic product we express $\gamma_{gr}^t(G\circ H)$ in terms of related invariant of the factors and find some explicit formulas for it. For the strong product, lower bounds on $\gamma_{gr}^t(G \boxtimes H)$ are proved as well as upper bounds for products of paths and cycles. For the Cartesian product we prove lower and upper bounds on the Grundy total domination number when factors are paths or cycles.