From inequalities relating symmetrizations of convex bodies to the diameter-width ratio for complete and pseudo-complete convex sets

Abstract

For a Minkowski centered convex compact set $K$ we define $\alpha (K)$ to be the smallest possible factor to cover $K\cap (-K)$ by a rescalation of $\mathrm{conv}(K\cup (-K))$ and give a complete description of the possible values of $\alpha (K)$ in the planar case in dependence of the Minkowski asymmetry of $K$. As a side product, we show that, if the asymmetry of $K$ is greater than the golden ratio, the boundary of $K$ intersects the boundary of its negative $-K$ always in exactly 6 points. As an application, we derive bounds for the diameter-width-ratio for pseudo-complete and complete sets, again in dependence of the Minkowski asymmetry of the convex bodies, tightening those depending solely on the dimension given in a recent result of Richter [10].