NEPS operations on cordial graphs (Q1801699)

Let nearly equal mean differing by at most one. A graph is cordial if there exists a partition of the vertex set into subsets of nearly equal sizes such that the set of edges connecting vertices from different subsets is nearly equal in size to the set of remaining edges. The author gives an adjacency matrix characterization of cordial graphs and investigates conditions under which the non-complete extended \(p\)-sum (NEPS; introduced by the reviewer and \textit{R. P. Lučić} [Publ. Fac. Elektrotechn. Univ. Belgrade, Sér. Math. Phys. 302-319, 67-71 (1970; Zbl 0209.282)] of cordial graphs is cordial.