Spectral expansion series with parenthesis for the nonself-adjoint periodic differential operators
Spectral expansion series with parenthesis for the nonself-adjoint periodic differential operators
In this paper we construct the spectral expansion for the differential operator generated in $L_{2}(-∞, ∞)$ by ordinary differential expression of arbitrary order with periodic complex-valued coefficients by introducing new concepts as essential spectral singularities and singular quasimomenta and using the series with parenthesis. Moreover, we find a criteria for …