On the spectra of non‐selfadjoint differential operators and their adjoints in direct sum spaces

The general ordinary quasidifferential expression M p of n th order, with complex coefficients and its formal adjoint on any finite number of intervals I p = ( a p , b p ), p = 1, …, N , are considered in the setting of the direct sums of ‐spaces of functions defined on each of the separate intervals. And a number of results concerning the location of the point spectra and regularity fields of general differential operators generated by such expressions are obtained.

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