A Remark on the Manhattan Distance Matrix of a Rectangular Grid

Consider the Quadratic Assignment Problem (QAP): given two matrices A and D, minimize {trace AXDX^T: X is a permutation matrix}. New lower bounds were obtained recently (Mittelmann and peng [8]) for the QAP where D is either the Manhattan distance matrix of a rectangular grid, or the Hamming distance of a hypercube. In this note, we show that the results in [8,11] extend to the case where D is a spherical Euclidean distance matrix, which includes the Manhattan distance matrix and the Hamming distance matrix as special cases.