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Rank numbers for bent ladders

Peter Richter;  Emily Leven;  Anh Tran;  Bryan Ek;  Jobby Jacob;  Darren A. Narayan — 2014

Discussiones Mathematicae Graph Theory

A ranking on a graph is an assignment of positive integers to its vertices such that any path between two vertices with the same label contains a vertex with a larger label. The rank number of a graph is the fewest number of labels that can be used in a ranking. The rank number of a graph is known for many families, including the ladder graph P2 × Pn. We consider how ”bending” a ladder affects the rank number. We prove that in certain cases the rank number does not change, and in others the rank...

Minimal rankings of the Cartesian product Kₙ ☐ Kₘ

Gilbert Eyabi;  Jobby Jacob;  Renu C. Laskar;  Darren A. Narayan;  Dan Pillone — 2012

Discussiones Mathematicae Graph Theory

For a graph G = (V, E), a function f:V(G) → 1,2, ...,k is a k-ranking if f(u) = f(v) implies that every u - v path contains a vertex w such that f(w) > f(u). A k-ranking is minimal if decreasing any label violates the definition of ranking. The arank number, ψ r ( G ) , of G is the maximum value of k such that G has a minimal k-ranking. We completely determine the arank number of the Cartesian product Kₙ ☐ Kₙ, and we investigate the arank number of Kₙ ☐ Kₘ where n > m.

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