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Structural characterization of classical and memristive circuits with purely imaginary eigenvalues

The hyperbolicity problem in circuit theory concerns the existence of purely imaginary eigenvalues in the linearization of the time‐domain description of the circuit dynamics. In this paper, we characterize the circuit configurations that, in a strictly passive setting, yield purely imaginary eigenvalues for all values of the capacitances and inductances. Our framework is based on branch‐oriented, semistate (differential‐algebraic) circuit models that capture explicitly the circuit topology, and use several notions and results from digraph theory. So‐called P‐structures arising in the analysis turn out to be the key element supporting our results. The analysis is shown to hold not only for classical (RLC) circuits but also for nonlinear circuits including memristors and other mem‐devices. Copyright © 2011 John Wiley & Sons, Ltd.