Abstract
We consider families of linear differential systems continuously depending on a real parameter with continuous (or piecewise continuous) coefficients on the half-line. The improperness set of such a family is defined as the set of all parameter values for which the corresponding systems in the family are Lyapunov improper. We show that a subset of the real axis is the improperness set of some family if and only if it is a G δσ -set. The result remains valid for families in which the matrices of the systems are bounded on the half-line. Almost the same result holds for families in which the parameter occurs only as a factor multiplying the system matrix: their improperness sets are the G δσ -sets not containing zero. For families of the last kind with bounded coefficient matrix, we show that their improperness set is an arbitrary open subset of the real line.
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Original Russian Text © E.A. Barabanov, 2009, published in Differentsial’nye Uravneniya, 2009, Vol. 45, No. 8, pp. 1067–1084.
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Barabanov, E.A. On the improperness sets of families of linear differential systems. Diff Equat 45, 1087–1104 (2009). https://doi.org/10.1134/S0012266109080011
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DOI: https://doi.org/10.1134/S0012266109080011