On dimensional rigidity of bar-and-joint frameworks

  • Authors:
  • Abdo Y. Alfakih

  • Affiliations:
  • Department of Mathematics and Statistics, University of Windsor, Windsor, Ont. Canada N9B 3P4

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2007

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Abstract

Let V={1,2,...,n}. A mapping p:V-R^r, where p^1,...,p^n are not contained in a proper hyper-plane is called an r-configuration. Let G=(V,E) be a simple connected graph on n vertices. Then an r-configuration p together with graph G, where adjacent vertices of G are constrained to stay the same distance apart, is called a bar-and-joint framework (or a framework) in R^r, and is denoted by G(p). In this paper we introduce the notion of dimensional rigidity of frameworks, and we study the problem of determining whether or not a given G(p) is dimensionally rigid. A given framework G(p) in R^r is said to be dimensionally rigid iff there does not exist a framework G(q) in R^s for s=r+1, such that @?q^i-q^j@?^2=@?p^i-p^j@?^2 for all (i,j)@?E. We present necessary and sufficient conditions for G(p) to be dimensionally rigid, and we formulate the problem of checking the validity of these conditions as a semidefinite programming (SDP) problem. The case where the points p^1,...,p^n of the given r-configuration are in general position, is also investigated.