An Eigenfunction Expansion for a Quadratic Pencil of a Schrödinger Operator with Spectral Singularities

The structure of the spectrum of a system of difference equations

“…It is known that one of the most important properties of non-selfadjoint differential equations is that of having spectral singularities [5][6][7][8][9][10][11]. In [12] it is proved by examples that non-selfadjoint difference equations of second order have spectral singularities.…”

Spectral Analysis of Non-Selfadjoint Discrete Schrödinger Operators with Spectral Singularities

“…Some problems of spectral theory of differential operators and some others types of operators with spectral singularities were studied in [1], [3], [5], [8], [9], [10], [11], [13], [17].…”

Non-selfadjoint matrix Sturm–Liouville operators with spectral singularities

“…From analyticity of f for Imk > À e4 , we obtain that all zeros of f in C þ have a finite multiplicity. Consequently the sets r d ðLÞ and r ss ðLÞ have a finite number of elements with a finite multiplicity.…”

“…Some problems of spectral theory of differential and some other types of operators with spectral singularities were also studied in [1,[3][4][5][6][7]15,16].…”