Constructively Factoring Linear Partial Differential Operators in Two Variables

We study conditions under which a partial differential operator of arbitrary order n in two variables or an ordinary linear differential operator admits a factorization with a first-order factor on the left.The process of factoring consists of recursively solving systems of linear equations subject to certain differential compatibility conditions.In the general case of partial differential operators, it is not necessary to solve a differential equation. In special degenerate cases, such as an ordinary differential operator, the problem eventually reduces to solving some Riccati equation(s). We give the factorization conditions explicitly for the second and third orders and in outline form for higher orders. __________ Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 145, No. 2, pp. 165–180, November, 2005.     

Spectral triples and manifolds with boundary

We investigate manifolds with boundary in noncommutative geometry. Spectral triples associated to a symmetric differential operator and a local boundary condition are constructed. We show that there is no tadpole for classical Dirac operators with a chiral boundary condition on spin manifolds.     

两类四阶微分算子积的自伴性研究

利用算子理论及矩阵运算方法,讨论了由两类不同的对称微分算式D~((4))+D~((2))+q_1(t)和D~((4))+q_2(t)(D=d/dt,t∈I=[a,b])生成的微分算子的积算子的自伴性,获得了积算子是自伴算子的充分必要条件.     

Equivalent operator preconditioning for elliptic problems

The numerical solution of linear elliptic partial differential equations most often involves a finite element or finite difference discretization. To preserve sparsity, the arising system is normally solved using an iterative solution method, commonly a preconditioned conjugate gradient method. Preconditioning is a crucial part of such a solution process. In order to enable the solution of very large-scale systems, it is desirable that the total computational cost will be of optimal order, i.e. proportional to the degrees of freedom of the approximation used, which also induces mesh independent convergence of the iteration. This paper surveys the equivalent operator approach, which has proven to provide an efficient general framework to construct such preconditioners. Hereby one first approximates the given differential operator by some simpler differential operator, and then chooses as preconditioner the discretization of this operator for the same mesh. In this survey we give a uniform presentation of this approach, including theoretical foundation and several practically important applications for both symmetric and nonsymmetric equations and systems, and some nonlinear examples in the context of Newton linearization. Dedicated to the memory of Gene Golub for his friendly manner and for his broad interest and significant impact on numerical analysis.     

Absolutely continuous spectrum of one random elliptic operator

We consider an elliptic random operator, which is the sum of the differential part and the potential. The potential considered in the paper is the same as the one in the Andersson model, however the differential part of the operator is different from the Laplace operator. We prove that such an operator has absolutely continuous spectrum on all of (0,∞).     

On the essential spectrum of hypoelliptic pseudo‐differential operators

We describe the essential spectrum of a hypoelliptic pseudo‐differential operator which is the sum of a constantcoefficients operator and an operator with coefficients vanishing at infinity. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Congruence of selfadjoint operators

Given a bounded selfadjoint operator a in a Hilbert space , the aim of this paper is to study the orbit of a, i.e., the set of operators which are congruent to a. We establish some necessary and sufficient conditions for an operator to be in the orbit of a. Also, the orbit of a selfadjoint operator with closed range is provided with a structure of differential manifold.      

Shape-preserving properties and asymptotic behaviour of the semigroup generated by the Black-Scholes operator

The paper is devoted to a careful analysis of the shape-preserving properties of the strongly continuous semigroup generated by a particular second-order differential operator, with particular emphasis on the preservation of higher order convexity and Lipschitz classes. In addition, the asymptotic behaviour of the semigroup is investigated as well. The operator considered is of interest, since it is a unidimensional Black-Scholes operator so that our results provide qualitative information on the solutions of classical problems in option pricing theory in Mathematical Finance. The paper is dedicated to Professor Luigi Albano on the occasion of his 70th birthday.     

Hypoellipticity of Nonlinear Partial Differential Equations

In this paper, we study the hypoellipticity problems for fully nonlinear panial differential equations of order m. For a solution u ∈ C^p_{loc}(Ω), if the linearized operator for the nonlinear equation on u satisfies some subelliptic conditions, we can deduce u ∈ C^∞(Ω) by using the paradifferential operator theory of J. -M. Bony.     

A Family of Irreducible Representations of the Witt Lie Algebra with Infinite-Dimensional Weight Spaces

We define a 4-parameter family of generically irreducible and inequivalent representations of the Witt Lie algebra on which the infinitesimal rotation operator acts semisimply with infinite-dimensional eigenspaces. They are deformations of the (generically indecomposable) representations on spaces of polynomial differential operators between two spaces of tensor densities on S ¹, which are constructed by composing each such differential operator with the action of a rotation by a fixed angle.     

Homogenization of Differential Operators

Abstract In this note, we present a method of constructing the homogenized operator for a general sequence ofdifferential operators. As an example, we construct the homogenized operator for a sequence of linear parabolicoperators.     

正则和奇异自共轭微分算子的变分公式化(英文)

1 IntroductionVariational methods offer an appealing approach to the analysis and com-putations associated with symmetric differential equations because they areclose1y connected to the under1ying physica1 principle of energy. Such methodshave been used to obtain the existence and uniqueness results, to investigateproperties of solutions [2], I61, [5], I7], and to compute solutions as welI as ei-genvalues [11, [41 fOr linear and nonlinear equations. The first step in applyinga variational me…     

向量值函数空间中J-对称算子的J-自伴延拓

给出了向量值函数空间中J-对称算子的J-自伴延拓的完全解析描述.我们应用Knowles理论,借助方程τ(y)=λ     

The finite rank perturbations of the product of Hankel and Toeplitz operators

In this paper we completely characterize when the product of a Hankel operator and a Toeplitz operator on the Hardy space is a finite rank perturbation of a Hankel operator, and when the commutator of a Hankel operator and a Toeplitz operators has finite rank.     

Existence of Solutions for Nonlinear Implicit Differential Equations: An Equilibrium Problem Approach

In this article, we study the existence of solutions for nonlinear implicit differential equations associated to a time-dependent pseudomonotone (respectively, quasimonotone) operator by using a new approach based on the theory of equilibrium \hboxproblems. More precisely, we first establish some existence results of solutions for mixed equilibrium problems where the \hboxbifunctions are, respectively, maximal monotone and \hboxpseudomonotone (quasimonotone) in the topological sense. Then, we write the nonlinear implicit differential equations in the form of a mixed equilibrium problem. By using the existence results for mixed equilibrium problems, we establish the existence of solutions of nonlinear implicit differential equations. This new approach provides some new and nice results which improve and unify most of the recent results obtained in this direction.     

On a Sturm-Liouville problem

In this paper we give a lower bound for the first eigenvalue of an ordinary differential operator which represents the radial part of the Laplace operator restricted to a spherical cap of a sphere, possibly of fractional dimension. The results are obtained by purely analytical methods.Research supported by CONICIT.     

A General Sampling Theorem Associated with Differential Operators

In this paper we prove a general sampling theorem associated with differential operators with compact resolvent. Thus, we are able to recover, through a Lagrange-type interpolatory series, functions defined by means of a linear integral transform. The kernel of this transform is related with the resolvent of the differential operator. Most of the well-known sampling theorems associated with differential operators are shown to be nothing but limit cases of this result.     

Self-adjoint realization of a class of third-order differential operators with an eigenparameter contained in the boundary conditions

The present paper deals with a class of third-order differential operators with eigenparameter dependent boundary conditions. Using operator theoretic formulation, the self-adjointness of this operator is proved, the properties of spectrum are investigated, its Green function and the resolvent operator are also obtained.     

Differential automorphisms for modular forms on Γ<Subscript>0</Subscript>(4)

If , then let M _k (Γ₀(4)) be the usual space of half integral weight modular forms. Ono constructed differential endomorphisms of M _k (Γ₀(4)) by using the usual differential operator. Here we construct a similar set of differential endomorphisms using a linear combination of the differential operator and the quasi-modular forms E ₂, E ₂|V ₂, and E ₂|V ₄. We compute a full set of eigenforms with eigenvalues, and we prove that these endomorphisms are in fact automorphisms. The author would like to thank the NSF for its support through the REGS program.