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Properties of distance functions on convex surfaces and applications

Jan Rataj, Luděk Zajíček (2011)

Czechoslovak Mathematical Journal

If X is a convex surface in a Euclidean space, then the squared intrinsic distance function dist 2 ( x , y ) is DC (d.c., delta-convex) on X × X in the only natural extrinsic sense. An analogous result holds for the squared distance function dist 2 ( x , F ) from a closed set F X . Applications concerning r -boundaries (distance spheres) and ambiguous loci (exoskeletons) of closed subsets of a convex surface are given.

Quasicrystals and almost periodic functions

Mariusz Zając (1999)

Annales Polonici Mathematici

We consider analogies between the "cut-and-project" method of constructing quasicrystals and the theory of almost periodic functions. In particular an analytic method of constructing almost periodic functions by means of convolution is presented. A geometric approach to critical points of such functions is also shown and illustrated with examples.

Quaternionic geometry of matroids

Tamás Hausel (2005)

Open Mathematics

Building on a recent paper [8], here we argue that the combinatorics of matroids are intimately related to the geometry and topology of toric hyperkähler varieties. We show that just like toric varieties occupy a central role in Stanley’s proof for the necessity of McMullen’s conjecture (or g-inequalities) about the classification of face vectors of simplicial polytopes, the topology of toric hyperkähler varieties leads to new restrictions on face vectors of matroid complexes. Namely in this paper...

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