Document Type : Research Paper


1 Department of Computer Science, Yazd University, Yazd, Iran.

2 Department of Computer Science, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran.


An outer connected dominating(OCD) set of a graph $G=(V,E)$ is a set $\tilde{D} \subseteq V$ such that every vertex not in $S$ is adjacent to a vertex in $S$, and the induced subgraph of $G$ by $V \setminus \tilde{D}$, i.e. $G [V \setminus \tilde{D}]$, is connected. The OCD number of $G$ is the smallest cardinality of an OCD set of $G$. The outer-connected bondage number of a nonempty graph G is the smallest number of edges whose removal from G results in a graph with a larger OCD number. Also, the outer-connected reinforcement number of G is the smallest number of edges whose addition to G results in a graph with a smaller OCD number. In 2018, Hashemi et al. demonstrated that the decision problems for the Outer-Connected Bondage and the Outer-Connected Reinforcement numbers are all NP-hard in general graphs. In this paper, we improve these results and show their hardness for bipartite graphs. Also, we obtain bounds for the outer-connected bondage number.