A combination difference scheme for the eigenvalue problem of the Laplace operator

The paper constructs and analyzes a combination difference scheme for numerical determination of the eigenvalues of the Laplace operator. The proposed scheme uses the two-sided (from above and from below) properties of variational-difference and ordinary difference schemes for the eigenvalue problem of the Laplace operator in convex domains. The half-sum of the two schemes in convex domains gives an O(h⁴) approximation to the exact eigenvalue. A summation representation formula is constructed as an implementation of the ten-point difference scheme.Kiev University. Nukus University. Turkmen Teachers College. Translated from Vychislitel'naya i Prikladnaya Matematika, No. 75, pp. 55–60, 1991.     

Calculation of eigenvalues of a discrete self-adjoint operator perturbed by a bounded operator

We generalize the method of regularized traces which calculates eigenvalues of a perturbed discrete operator for the case of an arbitrary multiplicity of eigenvalues of the unperturbed operator. We obtain a system of equations, enabling one to calculate eigenvalues of the perturbed operator with large ordinal numbers. As an example, we calculate eigenvalues of a perturbed Laplace operator in a rectangle.     

Eigenvalues and eigenfunctions of the Laplace operator on an equilateral triangle

A boundary value problem for the Laplace equation with Dirichlet and Neumann boundary conditions on an equilateral triangle is transformed to a problem of the same type on a rectangle. This enables us to use, e.g., the cyclic reduction method for computing the numerical solution of the problem. By the same transformation, explicit formulae for all eigenvalues and all eigenfunctions of the corresponding operator are obtained.     

Sublinear eigenvalue problems associated to the Laplace operator revisited

Eigenvalue problems involving the Laplace operator on bounded domains lead to a discrete or a continuous set of eigenvalues. In this paper we highlight the case of an eigenvalue problem involving the Laplace operator which possesses, on the one hand, a continuous family of eigenvalues and, on the other hand, at least one more eigenvalue which is isolated in the set of eigenvalues of that problem.     

Domain dependence of eigenvalues of elliptic type operators

The dependence on the domain for the Dirichlet eigenvalues of elliptic operators considered in bounded domains is studied. The proximity of domains is measured by a norm of the difference of two orthogonal projectors corresponding to the reference domain and the perturbed one; this allows to compare eigenvalues corresponding to domains that have non-smooth boundaries and different topology. The main result is an asymptotic formula in which the remainder is evaluated in terms of this quantity. Applications of this result are given. The results are new for the Laplace operator.     

Spectral bounds of the difference Laplace operator in non-rectangular regions

We consider the eigenvalue problem for a two-dimensional difference Laplace operator in non-rectangular regions (a curvilinear triangle, a curvilinear trapezoid, a circular segment). The dependence of the eigenvalues on the parameters of the regions is elucidated. The main result is the derivation of the spectral bounds of the difference operator. A lower bound for the minimum eigenvalue and an upper bound for the maximum eigenvalue are determined. The spectral bound is determined numerically for a series of non-rectangular regions. __________ Translated from Prikladnaya Matematika i Informatika, No. 23, pp. 94–113, 2006.     

Eigenvalue Problem for the Laplace Operator with Nonlocal Boundary Conditions

The suggested approach to maximizing the difference between the first and second eigenvalues of the Laplace operator is based on the introduction of nonlocal boundary conditions of a special form. It is shown that the difference can be arbitrarily large.     

Preconditioner for a discrete Laplace operator on a condensed grid

In this paper, it is proved that the discrete Laplace operator approximating a Dirichlet boundary value problem for a Poisson equation by a finite element method with piecewise-linear functions on an evenly condensed grid that is topologically equivalent to a rectangular grid (i.e., obtained by shifting the rectangular grid nodes) is equivalent, in the range, to the operator of a 5-point difference scheme on a uniform grid.     

Reliable computation of eigenvalues of the magnetostatic integral operator

Some variational problems in magnetostatics can be reformulated as eigenvalue problems for vector surface integral operators in appropriate function spaces, e.g., the magnetostatic integral operator is of considerable interest in the theory of permanent magnetization of compact bodies. In the case that the underlying surface is either a sphere, a spheroid, or a triaxial ellipsoid, explicit expressions for eigenvalues and eigenfunctions are well known. For the ellipsoid, these quantities are given in terms of Lamé functions and surface ellipsoidal harmonics. Since there is an apparent lack in literature we provide an new effective scheme for the reliable computation of these functions and of the corresponding eigenvalues of the magnetostatic operator.     

Fuchsian groups and small eigenvalues of the Laplace operator

In the spectral theory of automorphic functions, small eigenvalues (i.e., those lying in the interval [0, 1/4]) of the Laplace operator are of particular interest. In this note we give an upper bound for the number of small eigenvalues of the Laplace operator for noncompact Riemann surfaces, which are quotient spaces of the upper half plane by the action of Fuchsian groups of the first kind, and also of the multiplicity of small eigenvalues.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 122, pp. 24–29, 1982.     

A mixed method of subspace iteration for Dirichlet eigenvalue problems

A full multigrid scheme was used in computing some eigenvalues of the Laplace eigenvalue problem with the Dirichlet boundary condition. We get a system of algebraic equations with an aid of finite difference method and apply subspace iteration method to the system to compute first some eigenvalues. The result shows that this is very effective in calculating some eigenvalues of this problem.     

A Majorant for the Multiplicities of Eigenvalues of the Laplace Operator with Periodic Conditions

In the case of periodic conditions, we find explicit upper estimates in terms of power functions for the multiplicities r _n (p) of eigenvalues of the Laplace operator.     

Normalized graph Laplacians for directed graphs

We consider the normalized Laplace operator for directed graphs with positive and negative edge weights. This generalization of the normalized Laplace operator for undirected graphs is used to characterize directed acyclic graphs. Moreover, we identify certain structural properties of the underlying graph with extremal eigenvalues of the normalized Laplace operator. We prove comparison theorems that establish a relationship between the eigenvalues of directed graphs and certain undirected graphs. This relationship is used to derive eigenvalue estimates for directed graphs. Finally we introduce the concept of neighborhood graphs for directed graphs and use it to obtain further eigenvalue estimates.     

ON THE FIRST AND SECOND EIGENVALUES OF SCHRODINGER OPERATOR

The above boundary of the gap between the 2nd and 1st eigenvalues of Schrodinger operator and the above boundary of the ratio of the 2nd and 1st eigenvalues of Laplace operator are given.     

Graph Laplacians and topology

Laplace operators on metric graphs are considered. It is proven that for compact graphs the spectrum of the Laplace operator determines the total length, the number of connected components, and the Euler characteristic. For a class of non-compact graphs the same characteristics are determined by the scattering data consisting of the scattering matrix and the discrete eigenvalues.     

Universal inequalities for the eigenvalues of a power of the Laplace operator

In this paper, we obtain a new abstract formula relating eigenvalues of a self-adjoint operator to two families of symmetric and skew-symmetric operators and their commutators. This formula generalizes earlier ones obtained by Harrell, Stubbe, Hook, Ashbaugh, Hermi, Levitin and Parnovski. We also show how one can use this abstract formulation both for giving different and simpler proofs for all the known results obtained for the eigenvalues of a power of the Laplace operator (i.e. the Dirichlet Laplacian, the clamped plate problem for the bilaplacian and more generally for the polyharmonic problem on a bounded Euclidean domain) and to obtain new ones. In a last paragraph, we derive new bounds for eigenvalues of any power of the Kohn Laplacian on the Heisenberg group.     

On an eigenvalue for the Laplace operator in a disk with Dirichlet boundary condition on a small part of the boundary in a critical case

A boundary-value problem of finding eigenvalues is considered for the negative Laplace operator in a disk with Neumann boundary condition on almost all the circle except for a small arc of vanishing length, where the Dirichlet boundary condition is imposed. A complete asymptotic expansion with respect to a parameter (the length of the small arc) is constructed for an eigenvalue of this problem that converges to a double eigenvalue of the Neumann problem.     

Extremal spectral properties of Otsuki tori

Otsuki tori form a countable family of immersed minimal two‐dimensional tori in the unitary three‐dimensional sphere. According to the El Soufi‐Ilias theorem, the metrics on the Otsuki tori are extremal for some unknown eigenvalues of the Laplace‐Beltrami operator. Despite the fact that the Otsuki tori are defined in quite an implicit way, we find explicitly the numbers of the corresponding extremal eigenvalues. In particular we provide an extremal metric for the third eigenvalue of the torus.     

On the Eigenvalues of Finitely Perturbed Laplace Operators in Infinite Cylindrical Domains

In this paper, sufficient conditions for the existence of eigenvalues of a finitely perturbed Laplace operator in an infinite cylindrical domain and their asymptotics in the small parameter are given. Similar questions for tubes, i.e., deformed cylinders, are also considered.     

Asymptotics of simple eigenvalues and eigenfunctions for the Laplace operator in a domain with an oscillating boundary

The asymptotic behavior of solutions to spectral problems for the Laplace operator in a domain with a rapidly oscillating boundary is analyzed. The leading terms of the asymptotic expansions for eigenelements are constructed, and the asymptotics are substantiated for simple eigenvalues. The text was submitted by the authors in English.