A family of optimal identifying codes in Z2

  • Authors:
  • Iiro Honkala

  • Affiliations:
  • Department of Mathematics, University of Turku, Turku, Finland

  • Venue:
  • Journal of Combinatorial Theory Series A - Special issue in honor of Jacobus H. van Lint
  • Year:
  • 2006

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Abstract

Assume that G = (V, E) is a simple undirected graph, and C is a nonempty subset of V. For every v ∈ V, we denote lr(v) = {u ∈ C | dG(u, v) ≤ r}, where dG(u, v) denotes the number of edges on any shortest path between u and v. If the sets lr(v) for v ∈ V are pairwise different, and none of them is the empty set, we say that C is an r-identifying code in G. If C is r-identifying in every graph G' that can be obtained by adding and deleting edges in such a way that the number of additions and deletions together is at most t, the code C is called t-edge-robust. Let K be the graph with vertex set Z2 in which two different vertices are adjacent if their Euclidean distance is at most √2. We show that the smallest possible density of a 3-edge-robust code in K is r+1/2r+1 for all r 2.