Nonclassical Asymptotic Formulas and Approximation with an Arbitrary Order of Accuracy of Eigenvalues of the Sturm-Liouville Problem with Bitsadze-Samarskii Conditions

The Sturm-Liouville problem with Bitsadze-Samarskii conditions is analyzed in the paper. The study is performed in two directions: (i) construction and substantiation of a numerical-analytical method used for deriving eigenfunctions and eigenvalues and (ii) deriving sufficient conditions that are based on the FD-method, that has to provide real eigenvalues, and simplicity and convergence of the generalized nonclassical analytical series.     

Application of the Feynman-Kac path integral method in finding excited states of quantum systems

Group theory considerations and properties of a continuous path are used to define a failure tree procedure for finding eigenvalues of the Schrödinger equation using stochastic methods. The procedure is used to calculate the lowest excited state eigenvalues of eigenfunctions possessing anti-symmetric nodal regions in configuration space using the Feynman-Kac path integral method. Within this method the solution of the imaginary time Schrödinger equation is approximated by random walk simulations on a discrete grid constrained only by symmetry considerations of the Hamiltonian. The required symmetry constraints on random walk simulations are associated with a given irreducible representation and are found by identifying the eigenvalues for the irreducible representation corresponding to symmetric or antisymmetric eigenfunctions for each group operator. The method provides exact eigenvalues of excited states in the limit of infinitesimal step size and infinite time. The numerical method is applied to compute the eigenvalues of the lowest excited states of the hydrogenic atom that transform as Γ² and Γ⁴ irreducible representations. Numerical results are compared with exact analytical results.     

Two-dimensional approximations of three-dimensional eigenvalue problems in plate theory

The eigenvalues and eigenfunctions corresponding to the three-dimensional equations for the linear elastic equilibrium of a clamped plate of thickness 2?, are shown to converge (in a specific sense) to the eigenvalues and eigenfunctions of the well-known two-dimensional biharmonic operator of plate theory, as ? approaches zero. In the process, it is found in particular that the displacements and stresses are indeed of the specific forms usually assumed a priori in the literature. It is also shown that the limit eigenvalues and eigenfunctions can be equivalently characterized as the leading terms in an asymptotic expansion of the three-dimensional solutions, in terms of powers of ?. The method presented here applies equally well to the stationary problem of linear plate theory, as shown elsewhere by P. Destuynder.     

A method for obtaining bounds on eigenvalues and eigenfunctions by solving non-homogeneous integral equations

A new technique is presented for obtaining upper and lower bounds on eigenvalues and eigenfunctions for linear integral equations. The method is unique in that the bounds are obtained by solving non-homogeneous equations. In order to solve the non-homogeneous equations, non-linear sequence-to-sequence transformations are used to accelerate convergence of the Neumann series inside the radius of convergence and are used to “sum” the Neumann series outside the radius of convergence. Since the reciprocals of the eigenvalues appear as poles in the solution of the non-homogeneous equation, a very sensitive bounding criterion can be given. The method applies to quite general kernels, and has been successfully applied to symmetric and non-symmetric kernels. In addition, thek ^th eigenfunction may be obtained without a knowledge of the first (k?1) eigenvalues or eigenfunctions.     

The Lower/Upper Bound Property of Approximate Eigenvalues by Nonconforming Finite Element Methods for Elliptic Operators

This paper is a complement of the work (Hu et al. in arXiv:1112.1145v1[math.NA], 2011), where a general theory is proposed to analyze the lower bound property of discrete eigenvalues of elliptic operators by nonconforming finite element methods. One main purpose of this paper is to propose a novel approach to analyze the lower bound property of discrete eigenvalues produced by the Crouzeix–Raviart element when exact eigenfunctions are smooth. In particular, under some conditions on the triangular mesh, it is proved that the Crouzeix–Raviart element method of the Laplace operator yields eigenvalues below exact ones. Such a theoretical result explains most of numerical results in the literature and also partially answers the problem of Boffi (Acta Numerica 1–120, 2010). This approach can be applied to the Crouzeix–Raviart element of the Stokes eigenvalue problem and the Morley element of the buckling eigenvalue problem of a plate. As a second main purpose, a new identity of the error of eigenvalues is introduced to study the upper bound property of eigenvalues by nonconforming finite element methods, which is successfully used to explain why eigenvalues produced by the rotated $Q_1$ element of second order elliptic operators (when eigenfunctions are smooth), the Adini element (when eigenfunctions are singular) and the new Zienkiewicz-type element of fourth order elliptic operators, are above exact ones.     

Dispersion Analysis of Discontinuous Galerkin Schemes Applied to Poincaré, Kelvin and Rossby Waves

A technique for analyzing dispersion properties of numerical schemes is proposed. The method is able to deal with both non dispersive or dispersive waves, i.e. waves for which the phase speed varies with wavenumber. It can be applied to unstructured grids and to finite domains with or without periodic boundary conditions. We consider the discrete version L of a linear differential operator ℒ. An eigenvalue analysis of L gives eigenfunctions and eigenvalues (l _i ,λ _i ). The spatially resolved modes are found out using a standard a posteriori error estimation procedure applied to eigenmodes. Resolved eigenfunctions l _i ’s are used to determine numerical wavenumbers k _i ’s. Eigenvalues’ imaginary parts are the wave frequencies ω _i and a discrete dispersion relation ω _i =f(k _i ) is constructed and compared with the exact dispersion relation of the continuous operator ℒ. Real parts of eigenvalues λ _i ’s allow to compute dissipation errors of the scheme for each given class of wave. The method is applied to the discontinuous Galerkin discretization of shallow water equations in a rotating framework with a variable Coriolis force. Such a model exhibits three families of dispersive waves, including the slow Rossby waves that are usually difficult to analyze. In this paper, we present dissipation and dispersion errors for Rossby, Poincaré and Kelvin waves. We exhibit the strong superconvergence of numerical wave numbers issued of discontinuous Galerkin discretizations for all families of waves. In particular, the theoretical superconvergent rates, demonstrated for a one dimensional linear transport equation, for dissipation and dispersion errors are obtained in this two dimensional model with a variable Coriolis parameter for the Kelvin and Poincaré waves.     

Difetti ed eccessi degli autovalori del classico problema di «buckling»

The classical buckling eigenvalue problem for a square plate clamped along its boundary is here considered. By using the Rayleigh-Ritz method and the method of orthogonal invariants, we obtain upper and lower bounds for the first 60 eigenvalues. Numerical tables are given. The multiplicity of the first eigenvalues and the symmetries of the corresponding eigenfunctions are also studied.      

Numerical solution of singular ODE eigenvalue problems in electronic structure computations

We put forward a new method for the solution of eigenvalue problems for (systems of) ordinary differential equations, where our main focus is on eigenvalue problems for singular Schrödinger equations arising for example in electronic structure computations. In most established standard methods, the generation of the starting values for the computation of eigenvalues of higher index is a critical issue. Our approach comprises two stages: First we generate rough approximations by a matrix method, which yields several eigenvalues and associated eigenfunctions simultaneously, albeit with moderate accuracy. In a second stage, these approximations are used as starting values for a collocation method which yields approximations of high accuracy efficiently due to an adaptive mesh selection strategy, and additionally provides reliable error estimates. We successfully apply our method to the solution of the quantum mechanical Kepler, Yukawa and the coupled ODE Stark problems.     

具有一般耗散边界反馈的Euler-Bernoulli梁的指数镇定问题

讨论具有一般线性耗散边界反馈的Euler-Bernoulli梁的指数镇定问题.首先将所讨论 的系统化为抽象空间中的发展方程,并利用G0半群理论给出闭环系统解的存在唯一性.其次,对 相应的闭环系统特征方程进行详尽的讨论计算,得到了系统本征值的分布特性,从而利用Lassel 不变原理得到了闭环系统渐近稳定的充分必要条件.最后通过对闭环系统的本征值及其相应的 本征函数进行估计,导出了相应的闭环系统指数稳定的充分必要条件.     

MATLAB计算分子振动本征值和本征函数

分子动力学和分子光谱等的研究中,常常需要计算分子的振动本征值和振动本征函数。采用传统计算语言编程实现,往往繁琐而困难。MATLAB语言以矩阵为基本元素,自带的库函数可以高效便捷地解决计算其中涉及的许多数学问题。本文采用MATLAB语言计算了Morse势和双井(double well)势的振动本征值和振动本征函数。结果表明,MATLAB语言用于分子振动本征值和本征函数的计算,是一种简洁、高效的运算工具。所编制的程序具有普适性,只需对势能函数进行简单修改即可用于真实双原子分子的振动计算。     

Structural properties of matrix unitary reduction to semiseparable form

Abstract This paper concerns the study of a unitary transformation of a generic real symmetric matrix A into a semiseparable matrix. The problem is studied both theoretically and from an algorithmic point of view. In particular, we first give a formal proof of the existence of such a transformation and then we discuss its uniqueness, proving an implicit-Q theorem for semiseparable matrices. Lastly, we study structural properties of the factors of the QR-decomposition of a semiseparable matrix. These properties allow us to design a method based on QR iterations applied to a semiseparable matrix for reducing a symmetric matrix to semiseparable form. This method has the same asymptotic cost of the reduction of a symmetric matrix to tridiagonal form. Once the transformation is accomplished, to compute the eigenvalues each further QR iteration can be done in linear time.     

An hp finite element adaptive scheme to solve the Laplace model for fluid–solid vibrations

In this paper we introduce an hp finite element method to solve a two-dimensional fluid–structure spectral problem. This problem arises from the computation of the vibration modes of a bundle of parallel tubes immersed in an incompressible fluid. We prove the convergence of the method and a priori error estimates for the eigenfunctions and the eigenvalues. We define an a posteriori error estimator of the residual type which can be computed locally from the approximate eigenpair. We show its reliability and efficiency by proving that the estimator is equivalent to the energy norm of the error up to higher order terms, the equivalence constant of the efficiency estimate being suboptimal in that it depends on the polynomial degree. We present an hp adaptive algorithm and several numerical tests which show the performance of the scheme, including some numerical evidence of exponential convergence.     

Convergence of the spline function for functional-differential equation of neutral type

The existence, uniqueness and stability for the functional-differential equation of neutral type using spline of deficiency 3 with stepsize 3h spline function of degree four are presented in Ref. [1]. In this paper, we extend the study to the convergence of our proposed spline method. We prove that, if the local error is of order p, then the global error is of order p as well. Numerical examples are presented to illustrate the convergence of the method.     

A parametric analysis of discrete Hamiltonian functional maps

In this paper we develop an in-depth theoretical investigation of the discrete Hamiltonian eigenbasis, which remains quite unexplored in the geometry processing community. This choice is supported by the fact that Dirichlet eigenfunctions can be equivalently computed by defining a Hamiltonian operator, whose potential energy and localization region can be controlled with ease. We vary with continuity the potential energy and study the relationship between the Dirichlet Laplacian and the Hamiltonian eigenbases with the functional map formalism. We develop a global analysis to capture the asymptotic behavior of the eigenpairs. We then focus on their local interactions, namely the veering patterns that arise between proximal eigenvalues. Armed with this knowledge, we are able to track the eigenfunctions in all possible configurations, shedding light on the nature of the functional maps. We exploit the Hamiltonian-Dirichlet connection in a partial shape matching problem, obtaining state of the art results, and provide directions where our theoretical findings could be applied in future research.     

Bounds for theN lowest eigenvalues of fourth-order boundary value problems

We describe a method for the calculation of theN lowest eigenvalues of fourth-order problems inH ₀ ² (Ω). In order to obtain small error bounds, we compute the defects inH ⁻²(Ω) and, to obtain a bound for the rest of the spectrum, we use a boundary homotopy method. As an example, we compute strict error bounds (using interval arithmetic to control rounding errors) for the 100 lowest eigenvalues of the clamped plate problem in the unit square. Applying symmetry properties, we prove the existence of double eigenvalues.     

Lower Bounds for Eigenvalues of Elliptic Operators: By Nonconforming Finite Element Methods

The paper is to introduce a new systematic method that can produce lower bounds for eigenvalues. The main idea is to use nonconforming finite element methods. The conclusion is that if local approximation properties of nonconforming finite element spaces are better than total errors (sums of global approximation errors and consistency errors) of nonconforming finite element methods, corresponding methods will produce lower bounds for eigenvalues. More precisely, under three conditions on continuity and approximation properties of nonconforming finite element spaces we analyze abstract error estimates of approximate eigenvalues and eigenfunctions. Subsequently, we propose one more condition and prove that it is sufficient to guarantee nonconforming finite element methods to produce lower bounds for eigenvalues of symmetric elliptic operators. We show that this condition hold for most low-order nonconforming finite elements in literature. In addition, this condition provides a guidance to modify known nonconforming elements in literature and to propose new nonconforming elements. In fact, we enrich locally the Crouzeix-Raviart element such that the new element satisfies the condition; we also propose a new nonconforming element for second order elliptic operators and prove that it will yield lower bounds for eigenvalues. Finally, we prove the saturation condition for most nonconforming elements.     

A Spectral-Element Method for Transmission Eigenvalue Problems

We develop an efficient spectral-element method for computing the transmission eigenvalues in two-dimensional radially stratified media. Our method is based on a dimension reduction approach which reduces the problem to a sequence of one-dimensional eigenvalue problems that can be efficiently solved by a spectral-element method. We provide an error analysis which shows that the convergence rate of the eigenvalues is twice that of the eigenfunctions in energy norm. We present ample numerical results to show that the method convergences exponentially fast for piecewise stratified media, and is very effective, particularly for computing the few smallest eigenvalues.     

Creating a nilpotent pencil via deadbeat

We consider the problem of finding a square low-rank correction (λC ? B)F to a given square pencil (λE ? A) such that the new pencil λ(E ? CF) ? (A ? BF) has all its generalised eigenvalues at the origin. We give necessary and sufficient conditions for this problem to have a solution and we also provide a constructive algorithm to compute F when such a solution exists. We show that this problem is related to the deadbeat control problem of a discrete-time linear system and that an (almost) equivalent formulation is to find a square embedding that has all its finite generalised eigenvalues at the origin.     

Algebraic Perturbation Theory for Hydrogen Atom in Weak Electric Fields

An algorithm for symbolic calculation of eigenvalues and eigenfunctions of a hydrogen atom in weak electric fields is suggested. A perturbation theory scheme is constructed that is based on an irreducible infinite-dimensional representation of algebra so(4, 2) of the group of dynamical symmetry for the hydrogen atom [1]. The scheme implementation does not rely on the assumption that the independent variables of the perturbation operator can be separated, and fractional powers of parabolic quantum numbers are not used in the recurrent relations determining the operation of algebra generators on the corresponding basis of the irreducible representation [2]. A seventh-order correction to the energy spectrum of the hydrogen atom in a uniform electric field is given. The algorithm suggested is implemented in REDUCE 3.6 [4].