A crystallographic bar-joint framework C is shown to be almost periodically infinitesimally rigid if and only if it is strictly periodically infinitesimally rigid and the rigid unit mode (RUM) spectrum is a singleton. Moreover the almost periodic infinitesimal flexes of C are characterised in terms of a matrix-valued function on the d-torus determined by a full rank translation symmetry group and an associated motif of joints and bars.
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Special Issue on "Rigidity and Symmetry".
Guest Editor: Dr. Bernd Schulze, Department of Mathematics and Statistics, Fylde College, Lancaster University, Lancaster, LA1 4YF, UK