Geometrical embeddings of graphs

The scalar product dimension d ( G ) of a graph G is defined to be the minimum number m such that the vertices x of G can be represented by vectors x¯∈ R M with the property that xy is an edge of G iffx¯y¯⩾ t for some real threshold t . Graphs G with d(G) = 1 are characterized and d ( G ) is determined for a variety of graphs. The dimension is compared with the (related and well-known) threshold dimension. Two other variants (spherical and distance dimensions) are considered. Upper bounds for graphs with small maximum degree (or with small maximum degree of the complement) are established.