ENERGY FUNCTIONS FOR POLYGONAL KNOTS

Abstract

We define a scale-invariant energy function for polygonal knots in ℜ3 based on the minimum distances between segments. The energy is bounded below by 2π. (minimum crossing number of the knot type). For each knot type, there exists an ideal number of segments, from which can be made an ideal conformation of the knot having minimum energy among all polygons realizing that knot type. Results leading to this include the following: The energy of an n-segment polygon is greater than n; if energy is bounded then ratios of edge lengths and angles are bounded away from zero; changing knot type requires passing an infinite energy barrier. We implement an algorithm, with the feature that preserving knot-type is guaranteed, to discover local energy-minimizing conformations for a given number of segments, and present some of these examples.