On equicut graphs

The size sz(G) of an l_1-graph G=(V,E) is the minimum of n_f/t_f over all its possible l_1-embeddings f into n_f-dimensional hypercube with scale t_f. In terms of v=|V|, the sum of distances between all the pairs of vertices of G is at most sz(G) v^2/4 for v even, (resp. sz(G)(v-1)(v+1)/4 for v odd). This bound is reached if and only if G is an equicut graph, that is, G admits an l_1-embedding with column sums v/2, v even (resp. (v-1)/2 for v odd). Basic properties of equicut graphs are investigated. A construction of equicut graphs from l_1-graphs via a natural doubling construction is given. It generalizes several well-known constructions of polytopes and distance-regular graphs. Large families of examples, mostly related to polytopes and distance-regular graphs, are presented.