# American Institute of Mathematical Sciences

February  2014, 8(1): 35-52. doi: 10.3934/amc.2014.8.35

## An improved lower bound for $(1,\leq 2)$-identifying codes in the king grid

 1 Department of Mathematics, University of Johannesburg, Auckland Park 2006, South Africa 2 Department of Mathematics and Statistics, University of Turku, 20014 Turku, Finland 3 Institute of Mathematics, University of Liège, 4000 Liège, Belgium

Received  March 2012 Published  January 2014

We call a subset $C$ of vertices of a graph $G$ a $(1,\leq l)$-identifying code if for all subsets $X$ of vertices with size at most $\ell$, the sets $\{c\in C~|~\exists u\in X, d(u,c)\leq 1\}$ are distinct. The concept of identifying codes was introduced in 1998 by Karpovsky, Chakrabarty and Levitin. Identifying codes have been studied in various grids. In particular, it has been shown that there exists a $(1,\leq 2)$-identifying code in the king grid with density $\frac{3}{7}$ and that there are no such identifying codes with density smaller than $\frac{5}{12}$. Using a suitable frame and a discharging procedure, we improve the lower bound by showing that any $(1,\leq 2)$-identifying code of the king grid has density at least $\frac{47}{111}$. This reduces the gap between the best known lower and upper bounds on this problem by more than $56\%$.
Citation: Florent Foucaud, Tero Laihonen, Aline Parreau. An improved lower bound for $(1,\leq 2)$-identifying codes in the king grid. Advances in Mathematics of Communications, 2014, 8 (1) : 35-52. doi: 10.3934/amc.2014.8.35
##### References:
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##### References:
 [1] Y. Ben-Haim and S. Litsyn, Exact minimum density of codes identifying vertices in the square grid,, SIAM J. Discrete Math., 19 (2005), 69. doi: 10.1137/S0895480104444089. Google Scholar [2] I. Charon, I. Honkala, O. Hudry and A. Lobstein, The minimum density of an identifying code in the king lattice,, Discrete Math., 276 (2004), 95. doi: 10.1016/S0012-365X(03)00306-6. Google Scholar [3] I. Charon, O. Hudry and A. Lobstein, Identifying codes with small radius in some infinite regular graphs,, Electr. J. Combin., 9 (2002). Google Scholar [4] G. Cohen, S. Gravier, I. Honkala, A. Lobstein, M. Mollard, C. Payan and G. Zémor, Improved identifying codes for the grid,, Electr. J. Combin., 6 (1999). Google Scholar [5] G. Cohen, I. Honkala, A. Lobstein and G. Zémor, Bounds for codes identifying vertices in the hexagonal grid,, SIAM J. Discrete Math., 13 (2000), 492. doi: 10.1137/S0895480199360990. Google Scholar [6] G. Cohen, I. Honkala, A. Lobstein and G. Zémor, On codes identifying vertices in the two-dimensional square lattice with diagonals,, IEEE Trans. Comp., 50 (2001), 174. doi: 10.1109/12.908992. Google Scholar [7] D. W. Cranston and G. Yu, A new lower bound on the density of vertex identifying codes for the infinite hexagonal grid,, Electr. J. Combin., 16 (2009). Google Scholar [8] I. Honkala and T. Laihonen, Codes for identification in the king lattice,, Graphs Combin., 19 (2003), 505. doi: 10.1007/s00373-003-0531-2. Google Scholar [9] I. Honkala and T. Laihonen, On identifying codes in the triangular and square grids,, SIAM J. Comput., 33 (2004), 304. doi: 10.1137/S0097539703433110. Google Scholar [10] I. Honkala and T. Laihonen, On identifying codes in the hexagonal mesh,, Inform. Proc. Lett., 89 (2004), 9. doi: 10.1016/j.ipl.2003.09.009. Google Scholar [11] I. Honkala and T. Laihonen, On identification in the triangular grid,, J. Combin. Theory Ser. B, 91 (2004), 67. doi: 10.1016/j.jctb.2003.10.002. Google Scholar [12] M. G. Karpovsky, K. Chakrabarty and L. B. Levitin, On a new class of codes for identifying vertices in graphs,, IEEE Trans. Inform. Theory, 44 (1998), 599. doi: 10.1109/18.661507. Google Scholar [13] A. Lobstein, Watching systems, identifying, locating-dominating and discriminating codes in graphs: a bibliography,, available from , (). Google Scholar [14] M. Pelto, New bounds for $(r,\le 2)$-identifying codes in the infinite king grid,, Crypt. Commun., 2 (2010), 41. doi: 10.1007/s12095-009-0015-1. Google Scholar [15] S. Ray, R. Ungrangsi, F. De Pellegrini, A. Trachtenberg and D. Starobinski, Robust location detection in emergency sensor networks,, in Proc. IEEE INFOCOM 2003, (2003). doi: 10.1109/INFCOM.2003.1208941. Google Scholar
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