English

Rational Maps and Boundaries of Convex Hulls

Metric Geometry 2020-07-09 v2

Abstract

If Cn(Rd)C_n(\mathbb{R}^d) denotes the configuration space of nn distinct points in Rd\mathbb{R}^d, we construct a sequence of maps (fm),(f_m), m1m \geq 1, where fm:Cn(Rd)×RdRdf_m: C_n(\mathbb{R}^d) \times \mathbb{R}^d \to \mathbb{R}^d is real analytic, and has the property that for any xCn(Rd)\mathbf{x} \in C_n(\mathbb{R}^d) and any m1m \geq 1, the map fm(x,):RdRdf_m(\mathbf{x},-): \mathbb{R}^d \to \mathbb{R}^d is a rational map whose image lies in the convex hull of x\mathbf{x}. Our Approximation Conjecture is that for any xCn(Rd)\mathbf{x} \in C_n(\mathbb{R}^d), the image of the sphere Sd1S^{d-1} under our map fm(x,)f_m(\mathbf{x},-) is an approximation of the boundary of the convex hull of x\mathbf{x}. More precisely, we conjecture that limmdH(fm(x,)(Sd1),Conv(x))=0, \operatorname{lim}_{m \to \infty} d_H\left(f_m(\mathbf{x},-)(S^{d-1}), \,\partial \operatorname{Conv}(\mathbf{x}) \right) = 0, where dH(,)d_H(-,-) is the Hausdorff distance, Conv(x)\operatorname{Conv}(\mathbf{x}) is the convex hull of x\mathbf{x} and \partial is the boundary operator. Computer generated plots will be presented in this work.

Keywords

Cite

@article{arxiv.2004.04538,
  title  = {Rational Maps and Boundaries of Convex Hulls},
  author = {Joseph Malkoun},
  journal= {arXiv preprint arXiv:2004.04538},
  year   = {2020}
}

Comments

The paper is withdrawn: the conjecture here is false, but it led to another work with Peter J. Olver, arxiv:2007.03011 [math.MG], for which the corresponding statement is actually proved there