In-domatic number and some operations in digraphs

Let D be a digraph, a subset S of V(D) is called in-dominating set in D if for each vertex x ∈ V(D) \ S there is a vertex w ∈ S such that(x, w) ∈ A(D). An in-domatic partition of D is a partition of V(D) where all parts are in-dominating sets in D. The maximum number of parts of an in-domatic partition of D is the in-domatic number of D and it is denoted by d⁻(D). In this work, the in-domatic number for some families of digraphs such as complete digraphs, transitive digraphs, directed cycles and the cartesian product of two cycles, is calculated. Also, in-domatically critical digraphs are characterized. Additionally, the in-domatic partitions of the line digraph and some other operations which reflect the adjacency and incidence relations in digraphs are explored.