CFDP 1127

Matrices with Identical Sets of Neighbors


Publication Date: May 1996

Pages: 12


Given a generic m by n matrix A, a lattice point h in Z is a neighbor of the origin if the body {x : Ax < b}, with bi = max{0, aih}, i = 1, …, m, contains no lattice point other than 0 and h. The set of neighbors, N(A), is finite and Asymmetric. We show that if A’ is another matrix of the same size with the property that sign aih = sign ai’ h for every i and every h in N(A), then A’ has precisely the same set of neighbors as A. The collection of such matrices is a polyhedral cone, described by a finite set of linear inequalities, each such inequality corresponding to a generator of one of the cones Ci = pos(h in N(A): aih < 0}. Computational experience shows that Ci has “few” generators. We demonstrate this in the first nontrivial case n = 3, m = 4.

See CFP: 973