Packing radius vs covering radius

Let C_i, i = 1,2,... denote an infinite family of binary codes with length n_i, covering radius r_i, minimum distance d_i. Assume that the limit p (resp. δ) of the ratio r_i/n_i (resp. d_i/n_i) for large i exist and call it normalized covering radius (resp. distance). Our aim is to study the set Y₂ (resp. Y₂^lin) of points (ρ, δ) of the unit square achieved by binary families of codes (resp. of linear codes). We address the following questions for both domains: 1. bounds on the extreme points 2. convexity 3. continuity at the border. Both sets split naturally into four subdomains according to the position of ρ and δ w.r.t. 1/2.