 Orthonormal representation of a graph

Assign a real unit vector $u_v$ to each graph vertex, with $u_v\perp u_w$ whenever distinct vertices are nonadjacent. A handle is a further unit vector $h$. In the handle formulation of the Lovász number, one minimizes ${\max }_v|h\cdot u_v{|}^{-2}$ over representations and handles. Orthonormal here does not mean every pair of assigned vectors is orthogonal.