On the In-Out-Proper Orientations of Graphs

Abstract

An orientation of a graph $G$ is {\it in-out-proper} if any two adjacent vertices have different in-out-degrees, where the in-out-degree of each vertex is equal to the in-degree minus the out-degree of that vertex. The {\it in-out-proper orientation number} of a graph $G$, denoted by $\overleftrightarrow{\chi }(G)$, is ${\min }_{D\in \Gamma }{\max }_{v\in V(G)}|d_D^{\pm }(v)|$, where $\Gamma$ is the set of in-out-proper orientations of $G$ and $d_D^{\pm }(v)$ is the in-out-degree of the vertex $v$ in the orientation $D$.

Discrete Applied Mathematics (accepted)