Asymmetric proximity matrices: Proximity matrices in which the non-diagonal elements, in the ith row and jth column and the jth row and ith column, are not essentially equal. Examples are given by the number of marriages among men of one nationality and women of another, immigration statistics and the number of the citations of one journal by another.

Multidimensional scaling methods or techniques for such matrices generally rely on their canonical decom-position into the sum of a symmetric matrix and a skew symmetric matrix.