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Realization of Critical Eigenvalues for Scalar and Symmetric Linear Delay-Differential Equations

2008; Society for Industrial and Applied Mathematics; Volume: 7; Issue: 4 Linguagem: Inglês

10.1137/08071363x

1536-0040

Pietro-Luciano Buono, Victor G. LeBlanc,

Mathematical Biology Tumor Growth

This paper studies the link between the number of critical eigenvalues and the number of delays in certain classes of delay-differential equations. There are two main results. The first states that for k purely imaginary numbers which are linearly independent over the rationals, there exists a scalar delay-differential equation depending on k fixed delays whose spectrum contains those k purely imaginary numbers. The second result is a generalization of the first result for delay-differential equations which admit a characteristic equation consisting of a product of s factors of scalar type. In the second result, the k eigenvalues can be distributed among the different factors. Since the characteristic equation of scalar equations contain only exponential terms, the proof exploits a toroidal structure which comes from the arguments of the exponential terms in the characteristic equation. Our second result is applied to delay coupled $\mathbf{D}_n$-symmetric cell systems with one-dimensional cells. In particular, we provide a general characterization of delay coupled $\mathbf{D}_n$-symmetric systems with an arbitrary number of delays and cell dimension.