Characterizing r-perfect codes in direct products of two and three cycles

  • Authors:
  • Janja Jerebic;Sandi Klavžar;Simon Špacapan

  • Affiliations:
  • Department of Mathematics and Computer Science, PEF, University of Maribor, Koroška cesta 160, 2000 Maribor, Slovenia;Department of Mathematics and Computer Science, PEF, University of Maribor, Koroška cesta 160, 2000 Maribor, Slovenia;University of Maribor, FME, Smetanova 17, 2000 Maribor, Slovenia

  • Venue:
  • Information Processing Letters
  • Year:
  • 2005

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Abstract

An r-perfect code of a graph G = (V, E) is a set C ⊆ V such that the r-balls centered at vertices of C form a partition of V. It is proved that the direct product of Cm and Cn (r ≥ 1, m, n ≥ 2r + 1) contains an r-perfect code if and only if m and n are each a multiple of (r + 1)2 + r2 and that the direct product of Cm, Cn, and Cl (r ≥ 1, m, n, l ≥ 2r + 1) contains an r-perfect code if and only if m, n, and l are each a multiple of r3 + (r + 1)3. The corresponding r-codes are essentially unique. Also, r-perfect codes in C2r × Cn (r ≥ 2, n ≥ 2r) are characterized.