On utilizing the spectral representation of selfadjoint operators in Hilbert spaces, some error bounds in approximating $n$-time differentiable functions of selfadjoint operators in Hilbert Spaces via a Taylor's type expansion are given.

For selfadjoint elliptic operators in divergence form with ?-periodic coefficients of even order 2m ? 4 we approximate the resolvent energy operator norm $$ {\left\Vert \bullet \right\Vert}_{L^2\to {H}^m} a remainder ?2 as ? ? 0.

Hill’s method is a means to numerically approximate spectra of linear differential operators with periodic coefficients. In this paper, we address different issues related to the convergence of Hill’s method. We show the method does not produce any spurious approximations, and that for selfadjoint operators, the method converges in a restricted sense. Furthermore, assuming convergence of an eig...

This paper touches upon several traditional topics of 1D linear complex analysis including distribution of zeros of entire functions, completeness problem for complex exponentials and for other families of special functions, some problems of spectral theory of selfadjoint differential operators. Their common feature is the close relation to the theory of complex Fourier transform of compactly s...

We present recent progress in the understanding of the spectral and subelliptic properties of non-elliptic quadratic operators with application to the study of return to equilibrium for some systems of chains of oscillators. We then explain how these results allow to describe the spectral properties and to give sharp resolvent estimates for some classes of non-selfadjoint pseudodi erential oper...

We consider a Sturm-Liouville boundary value problem in a bounded domain D of Rn. By this is meant that the differential equation is given by a second order elliptic operator of divergent form in D and the boundary conditions are of Robin type on ∂D. The first order term of the boundary operator is the oblique derivative whose coefficients bear discontinuities of the first kind. Applying the me...

The aim of this paper is to investigate spectral properties of second order elliptic operators with measurable coefficients. Namely, we study the problems of L-independence of the spectrum and stability of the essential spectrum. The problem of L-independence of the spectrum for elliptic operators has a long history going back to B. Simon [30] where the question was posed for Schrödinger operat...

It is shown that the operators associated with the perturbed wave equation in IR n and with the elliptic operators with an indeenite weight function and mildly varying coeecients on IR n are similar to a selfadjoint operator in a Hilbert space. These operators have the whole IR as the spectrum. It is shown that they are positive operators in corresponding Krein spaces, and the whole problem is ...