Abstract
We characterize the self-adjoint domains of general even order linear ordinary differential operators in terms of real-parameter solutions of the differential equation. This for endpoints which are regular or singular and for arbitrary deficiency index. This characterization is obtained from a new decomposition of the maximal domain in terms of limit-circle solutions. These are the solutions which contribute to the self-adjoint domains in analogy with the celebrated Weyl limit-circle solutions in the second order Sturm–Liouville case. As a special case we obtain the previously known characterizations when one or both endpoints are regular.
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Hao, X., Sun, J., Wang, A. et al. Characterization of Domains of Self-Adjoint Ordinary Differential Operators II. Results. Math. 61, 255–281 (2012). https://doi.org/10.1007/s00025-011-0096-y
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DOI: https://doi.org/10.1007/s00025-011-0096-y