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Fahimeh Khosh-Ahang Ghasr

Publications and source records attributed to Fahimeh Khosh-Ahang Ghasr.

8 recordsLinked to original sources
arXiv2026

Bounds for (strong) Roman $k$-dominations

Motivated by resource defense models in networks, such as protecting territories with varying legion strengths, let $k \geq 2$ be an integer. Roman $k$-domination and strong Roman $k$-domination generalize Roman, double Roman, Italian, and double Italian domination to arbitrary number of legions. The main goal of this note is establishing sharp upper bounds for the Roman and strong Roman $k$-domination numbers of connected graphs. These bounds unify and extend prior results for $k=2$ and $k=3$. We also precisely characterize the graphs achieving these bounds.

math.CO↗
arXiv2026

Total Roman bondage number of a graph

A total Roman dominating function (TRDF) on a graph $G$ with no isolated vertices is a function $f:V(G)\to\{0,1,2\}$ such that every vertex $v$ with $f(v)=0$ has a neighbor assigned $2$, and the subgraph induced by $\{v:f(v)>0\}$ has no isolated vertices. The total Roman domination number $γ_{tR}(G)$ is the minimum weight of a TRDF on $G$. The total Roman bondage number $b_{tR}(G)$ is the minimum cardinality of an edge set $E'\subseteq E(G)$ such that $G-E'$ has no isolated vertices and $γ_{tR}(G-E')>γ_{tR}(G)$; if no such $E'$ exists, $b_{tR}(G)=\infty$. We prove that deciding whether $b_{tR}(G)\leq k$ is NP-complete for arbitrary graphs. We establish sharp bounds, including $γ_{tR}(G)+1\leq γ_{tR}(G-B)\leq γ_{tR}(G)+2$ for any $b_{tR}(G)$-set $B$ (both sharp), and $b_{tR}(G)\geq \max\{δ(G),b(G)\}$ when $γ_{tR}(G)=3β(G)$. We characterize graphs with $b_{tR}(G)=\infty$ and provide a necessary and sufficient condition for $b_{tR}(G)=1$. Exact values are determined for complete graphs, complete bipartite graphs, brooms, double brooms, wheels and wounded spiders. Further upper bounds are given in terms of order, diameter, girth, and structural features.

math.CO↗
arXiv2026

Grobner bases for determinantal facet ideals of simplicial complexes

We provide necessary and sufficient conditions for simplicial complexes whose determinantal facet ideals admit reduced Grobner bases under diagonal term orders. Building on and extending foundational results for binomial edge ideals and determinantal ideals, we introduce two new classes of simplicial complexes-strong closed and poor closed-that generalize the notion of closedness in higher dimensions. Our main theorem offers a unified framework that recovers and refines several known results, including those for unit interval graphs and determinantal ideals of complete graphs. In particular, we correct and generalize prior characterizations of Grobner bases for determinantal facet ideals, establishing radicality for strong closed complexes and providing a new proof for the Grobner basis of maximal minors.

math.AC↗
arXiv2025

Generalizations of interval and proper interval graphs for simplicial complexes

We introduce and investigate generalizations of interval and proper interval graphs to simplicial complexes, including strong interval, unit interval, and under closed variants. Through equivalent combinatorial and algebraic characterizations, we uncover hierarchies among these classes and extend key results to higher dimensions, such as the equivalence of closed and proper interval graphs. These formulations enable significant applications, including finding conditions for the sortability of d-independence complexes, constructions of normal Cohen-Macaulay domains linked to d-unit interval graphs, and forbidden subgraph theorems establishing chordality and d-claw-freeness. Our work advances the connections between graph theory, simplicial complexes, and commutative algebra, offering new insights into the algebraic underpinnings of combinatorial structures.

math.CO↗
arXiv2025

Powers of the edge ideals and matchings in hypergraphs

In this work, some combinatorial lower bound for regularity of powers of the edge ideal of a uniform hypergarph is gained. A family of hypergraphs whose regularity of edge ideal attains this bound and has a significant difference from the lower bounds heretofore obtained have also been introduced.

math.AC↗
arXiv2022

On a generalization of Roman domination with more legions

In this note, we generalize the concepts of (perfect) Roman and Italian dominations to (perfect) strong Roman and Roman k-domination for arbitrary positive integer k. These generalizations cover some of previous ones. After some comparison of their domination numbers, as a first study of these concepts, we study the (perfect, strong, perfect strong) Roman k-domination numbers of complete bipartite graphs.

math.CO↗
arXiv2020

Some interpretations for algebraic invariants of edge ideals of hypergraphs via combinatorial invariants

The present work is concerned with characterizing some algebraic invariants of edge ideals of hypergraphs. To this aim, firstly, we introduce some kinds of combinatorial invariants similar to matching numbers for hypergraphs. Then we compare them to each other and to previously existing ones. These invariants are used for characterizing or bounding some algebraic invariants of edge ideals of hypergraphs such as graded Betti numbers, projective dimension and Castelnouvo-Mumford regularity.

math.AC↗