February 9, 2023

# Doost Ali Mojdeh

Degree: Professor
Address: Department of Mathematics, University of Mazandaran, Babolsar, Iran
Education: Ph.D in Mathematics (Graph Theory and Combinatorics)
Phone: 011-35302448
Faculty: Faculty of Mathematical Sciences

## Research

 Title Further results on packing related parameters in graphs Type Article Keywords packing number, open packing number, independence number, Nordhaus-Gaddum inequality, total domination number. Journal Discussiones Mathematicae Graph Theory DOI https://doi.org/10.7151/dmgt.2262 Researchers a { color: #4f98b0; } a:hover { color: #ffab00; } a:link:visited { text-decoration: none; } Doost Ali Mojdeh (First researcher) , Babak Samadi (Second researcher) , Ismael Gonzalez Yero (Third researcher)

## Abstract

Given a graph $G=(V,E)$, a set $B\subseteq V(G)$ is a packing in $G$ if the closed neighborhoods of every pair of distinct vertices in $B$ are pairwise disjoint. The packing number $\rho(G)$ of $G$ is the maximum cardinality of a packing in $G$. Similarly, open packing sets and open packing number are defined for a graph $G$ by using open neighborhoods instead of closed ones. We give several results concerning the (open) packing number of graphs in this paper. For instance, several bounds on these packing parameters along with some Nordhaus-Gaddum inequalities are given. We characterize all graphs with equal packing and independence numbers and give the characterization of all graphs for which the packing number is equal to the independence number minus one. In addition, due to the \begin{color}{red}close\end{color} connection between the open packing and total domination numbers, we prove a new upper bound on the total domination number $\gamma_{t}(T)$ for a tree $T$ of order $n\geq 2$ improving the upper bound $\gamma_{t}(T)\leq(n+s)/2$ given by Chellali and Haynes in 2004, in which $s$ is the number of support vertices of $T$.