Numerical index of some polyhedral norms on the plane
Miguel Martı́n, Javier Merí · Linear and Multilinear Algebra · 2006
We give explicit formulae for the numerical index of some (real) polyhedral spaces of dimension two. Concretely, we calculate the numerical index of a family of hexagonal norms, two families of octagonal norms and the family of norms whose unit balls are regular polygons with an even number of vertices.