Uniform Embeddings for Robinson Similarity Matrices

A Robinson similarity matrix is a symmetric matrix where all entries in all rows and columns are increasing towards the diagonal. A Robinson matrix can be decomposed into the weighted sum of k adjacency matrices of a nested family of unit interval graphs. We study the problem of finding an embedding which gives a simultaneous unit interval embedding for all graphs in the family. This is called a uniform embedding. We give a necessary and sufficient condition for the existence of a uniform embedding, derived from paths in an associated graph. We also give an efficient combinatorial algorithm to find a uniform embedding or give proof that it does not exist, for the case where k = 2.