Network pearls climb stairs: a new game on graphs and its optimal solution

Abstract

Let $G$ be a graph, and $a$ and $b$ be integers. Suppose there are infinite number of stairs, numbering level $0$, level $1$, etc. How do you place every vertex of the graph $G$ on a level as high as possible such that a vertex placed on level $i$ should have at least $i-b$ neighbors among the vertices placed on level $i$ and above while have at least $i$ neighbors among the vertices placed on level $i-a$ and above? This new game on graphs is referred to as ``network pearls climb stairs". In this paper, we develop a more general theory, notably a correspondence between structure and dynamics, which particularly leads to the optimal solution of the game. Moreover, as $a$ and $b$ vary, the corresponding level numbers for a vertex obviously provide a structural profile (or spectrum) for the vertex the applications of which are worthy of further study.

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