tailieunhanh - Báo cáo toán học: "Jamming and geometric representations of graphs"

Tuyển tập các báo cáo nghiên cứu khoa học về toán học trên tạp chí toán học quốc tế đề tài: Jamming and geometric representations of graphs. | Jamming and geometric representations of graphs Werner Krauth1 and Martin Loebl2 1CNRS-Laboratoire de Physique Statistique Ecole Normale Superieure Paris 2Department of Applied Mathematics and Institute for Theoretical Computer Science Charles University Prague loebl@ Submitted Apr 29 2005 Accepted Jun 27 2006 Published Jul 11 2006 Mathematics Subject Classifications 05C62 05C70 Abstract We expose a relationship between jamming and a generalization of Tutte s barycentric embedding. This provides a basis for the systematic treatment of jamming and maximal packing problems on two-dimensional surfaces. 1 Introduction In a seminal paper 1 W. T. Tutte addressed the problem of how to embed a three-connected planar graph in the plane. He proposed to fix the positions of the vertices of one face outer vertices as the vertices of a convex n-gon and to let the other inner vertices of the graph to be positioned into the barycenters of their neighbors see Fig. 1 . Figure 1 Barycentric embedding of a graph with N 13 vertices three outer vertices . The barycentric embedding is unique. If we denote by r1 . rN the positions of vertices of a graph with N vertices then the barycentric embedding minimizes the energy E E r. - r r2 edges ij THE ELECTRONIC JOURNAL OF COMBINATORICS 13 2006 R56 1 proportional to the mean squared edge length over the positions of the inner vertices see 1 . The purpose of this paper is to study jamming a problem of importance for the physics of granular materials and of glasses 2 3 4 which also has many applications in mathematics and computer science 5 . We expose a relationship between jamming and a generalization of the barycentric embedding and provide a basis for the systematic treatment of jamming on twodimensional surfaces. We first informally describe our results and leave the formal definitions to the following sections. A set of non-overlapping disks of equal radius may contain a sub-set of disks which do not .

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