## On the spectra of non-selfadjoint differential operators and their adjoints in direct sum spaces.(English)Zbl 1023.34076

Summary: The general ordinary quasidifferential expression $$M_p$$ of $$n$$th order, with complex coefficients and its formal adjoint $$M_p^+$$ on any finite number of intervals $$I_{p}=(a_p,b_p)$$, $$p=1,\dots N$$, are considered in the setting of the direct sums of $$L_{w_p}^{2}(a_p,b_p)$$-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.

### MSC:

 34L05 General spectral theory of ordinary differential operators 34L15 Eigenvalues, estimation of eigenvalues, upper and lower bounds of ordinary differential operators 47E05 General theory of ordinary differential operators
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