Criticality for the Gehring link problem

By Jason H. Cantarella, Joseph H. G. Fu, Robert B. Kusner, John M. Sullivan Jr., Nancy C. Wrinkle. 2004

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In 1974, Gehring posed the problem of minimizing the length of two linked curves separated by unit distance. This constraint can be viewed as a measure of thickness for links, and the ratio of length over thickness as the ropelength. In this paper we refine Gehring's problem to deal with links in a fixed link-homotopy class: we prove ropelength minimizers exist and introduce a theory of ropelength criticality. Our balance criterion is a set of necessary and sufficient conditions for criticality, based on a strengthened, infinite-dimensional version of the Kuhn--Tucker theorem. We use this to prove that every critical link is C^1 with finite total curvature. The balance criterion also allows us to explicitly describe critical configurations (and presumed minimizers) for many links including the Borromean rings. We also exhibit a surprising critical configuration for two clasped ropes: near their tips the curvature is unbounded and a small gap appears between the two components. These examples reveal the depth and richness hidden in Gehring's problem and our natural extension.

Subfields: Civil and Structural Engineering, Computational Theory and Mathematics, Geometry and Topology

View Paper: https://www.semanticscholar.org/paper/460f784272e1e874e840807acd1e09ae47d42fb8

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In Computational Theory and Mathematics

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  2. H. von der Mosel

In Geometry and Topology

  1. Pawel Strzelecki
  2. H. von der Mosel

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