Differential-operator Equations Research Articles

Asymptotics and Quotient Spaces of Solutions of Operator-Difference Equations and Differential Equations with Small Delay

Formerly, in order to conduct the in-depth study of differential equations with delay, the author proposed the method of splitting the solution space reducing such equations to the systems of operator-difference equations. Using this method, the author assumed new conditions, i.e. the absolute domains for coefficients sufficient for the existence of special (slowly changing) solutions, and proved the presence of approximating and asymptotically approximating properties in them, as well as the asymptotic one-dimensional space of solutions of the initial problems for linear scalar differential equations with insignificantly retarded argument and the corresponding operator-difference equation systems (special solutions correspond, to the solutions with a slowly changing first component and a relatively small second component). For the purposes of the single-point representation of the obtained results and other data related to the theory of dynamic systems (the distance between the solution values tends to zero alongside the unlimited increase in argument), throughout this research paper the author uses the concept of the asymptotic equivalence of solutions for dynamic systems, as it was introduced by the author in their previous research. In order to shape the new mathematical objects, the concept of asymptotic Hausdorff equivalence of solutions for dynamic systems is introduced (the distance between solution values tends to zero with unlimited increase in argument of one solution and monotonic transformation of argument of another solution).

Conditions of solvability of the nonlocal boundary-value problem for a differential-operator equation with weak nonlinearity

We study the solvability of a nonlocal boundary-value problem for a differential equation with nonlinearity. The linear part of the equation has complex coefficients which together with the coefficient in nonlocal conditions are considered to be the parameters of the problem. The area of change of each parameter is limited by a complex circle with its center at the origin. The nonlinear part of the equation is given by a smooth function that satisfies, together with its derivatives, some conditions of growth in the Dirichlet--Fourier space scale. The proofs are based on the differentiable Nash--Moser iteration scheme, where the main difficulty is to get estimates of the interpolation type for the inverse linearized operators obtained at each step of the iteration. The estimation is connected with the problem of small denominators which is solved, by using a metric approach on the set of parameters of the problem.

Approximate Solutions of One Abstract Cauchy Problem

We find approximate solutions of the Cauchy problem for a differential-operator equation of hyperbolic type with degeneration in a Hilbert space. In terms of these approximations, we give a characteristic of the Gevrey classes for a nonnegative self-adjoint operator.

Existence Results for a Class of Nonlinear Hadamard Fractional with p-Laplacian Operator Differential Equations

In this study, we are concerned with the existence and uniqueness of solution for some nonlinear Hadamard fractional differential equations. Our results are based on different classical fixed point theorems. Some useful examples are presented in order to illustrate the validity of our main results.

THE NON-LOCAL TIME PROBLEM FOR ONE CLASS OF PSEUDODIFFERENTIAL EQUATIONS WITH SMOOTH SYMBOLS

In this paper we investigate the differential-operator equation $$ \partial u (t, x) / \partial t + \varphi (i \partial / \partial x) u (t, x) = 0, \quad (t, x) \in (0, + \infty) \times \mathbb {R} \equiv \Omega, $$ where the function $ \varphi \in C ^ {\infty} (\mathbb {R}) $ and satisfies certain conditions. Using the explicit form of the spectral function of the self-adjoint operator $ i \partial / \partial x $, in $ L_2 (\mathbb {R}) $ it is established that the operator $ \varphi (i \partial / \partial x) $ can be understood as a pseudodifferential operator in a certain space of type $ S $. The evolution equation $ \partial u / \partial t + \sqrt {I- \Delta} u = 0 $, $ \Delta = D_x ^ 2 $, with the fractionation differentiation operator $ \sqrt { I- \Delta} = \varphi (i \partial / \partial x) $, where $ \varphi (\sigma) = (1+ \sigma ^ 2) ^ {1/2} $, $ \sigma \in \mathbb {R} $ is attributed to the considered equation. Considered equation is a nonlocal multipoint problem with the initial function $ f $, which is an element of a space of type $ S $ or type $ S '$ which is a topologically conjugate with a space of type $ S $ space. The properties of the fundamental solution of such a problem are established, the correct solvability of the problem in the half-space $ t> 0 $ is proved, the representation of the solution in the form of a convolution of the fundamental solution with the initial function is found, the behavior of the solution $ u (t, \cdot) $ for $ t \to + \infty $ (solution stabilization) in spaces of type $ S '$.

Computation of green’s tensor and wave propagation in the random granular elastic medium

A linear differential operator equation involving randomly variable field parameters, characterising the heterogeneous granular elastic medium is considered. The appropriate Green’s tensor is evaluated for the non-deterministic operator equations in the form of Fourier integrals in the frequency space; the exact evaluation is carried out to obtain the 36 components of Green’s tensor. The problem of wave propagation in the random granular elastic medium is then carried out with the help of the associated Green’s tensor. The effect of random variation of parameters on wave propagation in the granular elastic medium is examined. Dispersion equations have been analysed in details.

Існування періодичних розв’язків в системі нелінійних осциляторів зі степеневими потенціалами на двовимірній ґратці

This article is devoted to the study of an infinite-dimensional Hamiltonian system, which describes an infinite system of linearly coupled nonlinear oscillators on a two-dimensional lattice. This system is a counteble system of ordinary differential equations. It is convenient to consider this system as a differential-operator equation in Hilbert space of real two-way sequences. The problem of existence of periodic solutions for such systems with power potential is considered. The main conditions for the existence of these solutions are the spatial periodicity of the coefficients of the linear interaction of oscillators and the positivity of this operator. This article shows that periodic solutions can be constructed using the constained minimization method. For this, a functional is constructed whose critical points are the desired periodic solutions. This functional is represented as the difference between the quadratic and non-quadratic parts. Next, we consider the problem of constrained minimization of the quadratic part of the functional under the condition that the non-quadratic part is constant. Using the Lagrange multiplier method, it was found that the periodic solutions of this system linearly depend on the solutions of the considered problem of constrained minimization, in particular, the coefficient of linear dependence is expressed in terms of the Lagrange multiplier. Using a discrete version of the concentration compactness principle, it is proved that the problem of constrained minimization under consideration has a solution, and therefore, there are periodic solutions of the original system. In particular, it is shown that for an arbitrary minimizing sequence of the quadratic part of the constructed functional, the possibility of «concentration» of the concentration compactness principle is satisfies, which allowed to prove the boundedness of this sequence. Moreover, it is proved that for sufficiently large values of periods these solutions are not constant

Solvability Conditions for the Nonlocal Boundary-Value Problem for a Differential-Operator Equation with Weak Nonlinearity in the Refined Sobolev Scale of Spaces of Functions of Many Real Variables

We study the solvability of the nonlocal boundary-value problem for a differential equation with weak nonlinearity. By using the Nash–Mozer iterative scheme, we establish the solvability conditions for the posed problem in the Hilbert H¨ormander spaces of functions of several real variables, which form a refined Sobolev scale.

Separable Differential Operators with Parameters

In this paper, we study boundary value problems for parameter-dependent elliptic differential-operator equations with variable coefficients in smooth domains. Uniform regularity properties and Fredholmness of this problem are obtained in vector-valued $$ {\text{L}}_{p} $$ -spaces. We prove that the corresponding differential operator is positive and is a generator of an analytic semigroup. Then, via maximal regularity properties of the linear problem, the existence and uniqueness of the solution to the nonlinear elliptic problem is obtained. As an application, we establish maximal regularity properties of the Cauchy problem for abstract parabolic equations, Wentzell–Robin-type mixed problems for parabolic equations, and anisotropic elliptic equations with small parameters.

Direct and Converse Theorems for Iterative Methods of Solving Irregular Operator Equations and Finite Difference Methods for Solving Ill-Posed Cauchy Problems

Results obtained in recent years concerning necessary and sufficient conditions for the convergence (at a given rate) of approximation methods for solutions of irregular operator equations are overviewed. The exposition is given in the context of classical direct and converse theorems of approximation theory. Due to the proximity of the resulting necessary and sufficient conditions to each other, the solutions on which a certain convergence rate of the methods is reached can be characterized nearly completely. The problems under consideration include irregular linear and nonlinear operator equations and ill-posed Cauchy problems for first- and second-order differential operator equations. Procedures for stable approximation of solutions of general irregular linear equations, classes of finite-difference regularization methods and the quasi-reversibility method for ill-posed Cauchy problems, and the class of iteratively regularized Gauss–Newton type methods for irregular nonlinear operator equations are examined.

Extremal Shift in a Problem of Tracking a Solution of an Operator Differential Equation

A control problem for an operator differential equation in a Hilbert space is considered. The problem consists in constructing an algorithm generating a feedback control and guaranteeing that the solution of the equation follows a solution of another equation, which is subject to an unknown disturbance. We assume that both equations are given on an infinite time interval and the unknown disturbance is an element of the space of square integrable functions; i.e., the perturbation may be unbounded. We construct two algorithms based on elements of the theory of ill-posed problems and the extremal shift method known in the theory of positional differential games. The algorithms are stable with respect to information noises and calculation errors. The first and second algorithms can be used in the cases of continuous and discrete measurement of solutions, respectively.

Sufficient conditions for regular solvability of an arbitrary order operator-differential equation with initial-boundary conditions

On this paper, for an arbitrary order operator-differential equation with the weight e^{frac{-alpha t}{2}}, alpha in (-infty ,+ infty ), in the space W^{n+m}_{2}(R_{+};H), we attain sufficient conditions for the well-posedness of a regular solvable of the boundary value problem. These conditions are provided only by the operator coefficients of the investigated equation where the leading part of the equation has multiple characteristics. We prove the connection between the lower bound of the spectrum of the higher-order differential operator in the main part and the exponential weight and also obtain estimations of the norms of operator intermediate derivatives. We apply the results of this paper to a mixed problem for higher-order partial differential equations (HOPDs).

New Results on Elliptic Equations with Nonlocal Boundary Coefficient-Operator Conditions in UMD Spaces: Noncommutative Cases

This paper is devoted to the abstract study of operational second-order differential equations of elliptic type with nonregular coefficient-operator boundary conditions in a non-commutative framework. The study is performed when the second member f belongs to $$L^{p}(0,1;X)$$, with general $$p\in ]1,+\infty [$$, X being a UMD Banach space. We give some new results by using semigroups and interpolation theory. Existence, uniqueness and optimal regularity of the classical and semi-classical solution are proved. This paper improves naturally the ones studied in the commutative case by Hammou et al. (Mediterr J Math, 1669–1683, 2015).

Asymptotic Behavior of Eigenvalues of a Boundary Value Problem for a Second-Order Elliptic Differential–Operator Equation with Spectral Parameter in the Equation and a Boundary Condition

In a separable Hilbert space $$H$$, we study the asymptotic behavior of eigenvalues of a boundary value problem for second-order elliptic differential–operator equations for the case in which the spectral parameter occurs in the equation quadratically and one of the boundary conditions is a quadratic trinomial in the same spectral parameter. We derive asymptotic formulas for the eigenvalues of this boundary value problem. An application of the abstract results obtained here to elliptic boundary value problems is indicated.

Two point inverse problems for singular first order operator-differential equations

We examine solvability questions of inverse problems on recovering a right-hand side of a special form in an operator-differential equation of the first order defined in some Hilbert space. An operator at the derivative with respect to time can have a nontrivial kernel and the spectrum of the corresponding linear pencil can contain unbounded subsets of the right and left half-planes. The boundary data are the values of a solution at the initial and final moments of time. Existence and uniqueness theorems are obtained under some conditions for the data.

On Fredholm property of a boundary value problem for third order operator-differential equations

On Fredholm property of a boundary value problem for third order operator-differential equations

Manypoint Boundary Value Problems for Elliptic Differential-Operator Equations with Interior Singularities

In this work, a elliptic differential-operator equation together with boundary-transmission conditions is considered on two disjoint intervals. The boundary-transmission conditions may contain finite number interior points and abstract linear operators. We establish such important properties as coerciveness and Fredholmness of the problem under consideration. Moreover, we prove that the system of root functions forms an Abel basis in the corresponding Hilbert space.

Basins of Attraction and Stability of Nonlinear Systems’ Equilibrium Points

The system of differential and operator equations is considered. This system is assumed to enjoy an equilibrium point. The Cauchy problem with the initial condition with respect to one of the desired functions is formulated. The second function controls the corresponding nonlinear dynamic process. The sufficient conditions of the global classical solution’s existence and stabilisation at infinity to the equilibrium point are formulated in the main theorem. Solution can be constructed by the method of successive approximations. If the conditions of the main theorem are not satisfied, then several solutions may exist. Some solutions can blow-up in a finite time, while others stabilise to an equilibrium point. The special case of considered systems of differential-operator equations are nonlinear systems of differential-algebraic equations which model various nonlinear phenomena in power systems, chemical processes and many other processes.

Solvability of initial-boundary value problem of a multiple characteristic fifth-order operator-differential equation

In this study, we establish existence-uniqueness of a vector function in appropriate Sobolev-type space for a boundary value problem of a fifth-order operator differential equation. Proper conditions are obtained for the given problem to be well-posed. Much effort is devoted to develop the association between these conditions and the operator coefficients of the investigated equation. In this paper, accurate estimates of the norms of the intermediate derivatives operators are presented and used to determine the solvability conditions.

Two Point Problem for the Abstract Differential Equation of the Second Order

The work is about the study of the boundary value problem for the second-order differential operator equation. The problem is investigated for conditional correctness. Theorems on uniqueness and conditional stability are proved. An approximate solution of the problem by the quasi-inversion method is constructed, an estimate of the norm between the exact and approximate solutions is obtained, and a formula for the regularization parameter is found.