On a Dispersion Problem in Grid Labeling

  • Authors:
  • Minghui Jiang;Vincent Pilaud;Pedro J. Tejada

  • Affiliations:
  • mjiang@cc.usu.edu;vpilaud@math.jussieu.fr;p.tejada@aggiemail.usu.edu

  • Venue:
  • SIAM Journal on Discrete Mathematics
  • Year:
  • 2012

Quantified Score

Hi-index 0.00

Visualization

Abstract

Given $k$ labelings of a finite $d$-dimensional cubical grid, define the combined distance between two labels to be the sum of the $\ell_1$-distance between the two labels in each labeling. We want to construct $k$ labelings which maximize the minimum combined distance between any two labels. When $d=1$, this can be interpreted as placing $n$ nonattacking rooks in a $k$-dimensional chessboard of size $n$ in such a way to maximize the minimum $\ell_1$-distance between any two rooks. Rook placements are also known as Latin hypercube designs in the literature. In this paper, we revisit this problem with a more geometric approach. Instead of providing explicit but complicated formulas, we construct rook placements in a $k$-dimensional chessboard of size $n$ as certain lattice-like structures for certain well-chosen values of $n$. Then, we extend these constructions to any values of $n$ using geometric arguments. With this method, we present a clean and geometric description of the known optimal rook placements in the two-dimensional square grid. Furthermore, we provide asymptotically optimal constructions of $k$ labelings of $d$-dimensional cubical grids which maximize the minimum combined distance. Finally, we discuss the extension of this problem to labelings of an arbitrary graph. We prove that deciding whether a graph has two labelings with combined distance at least $3$ is at least as hard as graph isomorphism.