Taut and Tense Networks

Geometrical constructions using flexible cords have been known since the earliest days of recorded mathematics. In this paper we introduce rigorous definitions for two classes of string networks. A taut network is one in which all cords are tight in every possible configuration; a tense network has configurations in which one or more cords are not tight, but is externally constrained to avoid such configurations. We show that taut networks compute only affine linear functions and subspaces, whereas tense networks (which are closely related to linkages) can trace any algebraic curve.