Rigid tensegrity labelings of graphs

  • Authors:
  • Tibor Jordán;András Recski;Zoltán Szabadka

  • Affiliations:
  • Department of Operations Research, Eötvös University, Pázmány Péter sétány 1/C, 1117 Budapest, Hungary;Department of Computer Science and Information Theory, Budapest University of Technology and Economics, H-1521 Budapest, Hungary;Department of Operations Research, Eötvös University, Pázmány Péter sétány 1/C, 1117 Budapest, Hungary

  • Venue:
  • European Journal of Combinatorics
  • Year:
  • 2009

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Abstract

Tensegrity frameworks are defined on a set of points in R^d and consist of bars, cables, and struts, which provide upper and/or lower bounds for the distance between their endpoints. The graph of the framework, in which edges are labeled as bars, cables, and struts, is called a tensegrity graph. It is said to be rigid in R^d if it has an infinitesimally rigid realization in R^d as a tensegrity framework. The characterization of rigid tensegrity graphs is not known for d=2. A related problem is how to find a rigid labeling of a graph using no bars. Our main result is an efficient combinatorial algorithm for finding a rigid cable-strut labeling of a given graph in the case when d=2. The algorithm is based on a new inductive construction of redundant graphs, i.e. graphs which have a realization as a bar framework in which each bar can be deleted without increasing the degree of freedom. The labeling is constructed recursively by using labeled versions of some well-known operations on bar frameworks.