The asymptotics of solutions of singularly perturbed functional differential equations: Distributed and concentrated delays are different

This paper illustrates the differences between systems with distributed delays and systems having only concentrated delays in what concerns the asymptotic rates of solutions of singularly perturbed linear retarded functional differential equations. An example of a system with distributed delays shows that the introduction of a “slow” variable coupled with the “fast” variable may decrease the asymptotic rates of solutions observed when the perturbation parameter is close to zero. Such a situation cannot happen for ordinary differential equations, or even for differential-difference equations.     

Approximate controllability of neutral systems with delays in control

The convergence of solutions of singularly perturbed systems of linear retarded functional differential equations to solutions of the associated degenerate problem is discussed in connection with the geometry of the flow in phase spaces defined in terms of square-integrable functions.     

On the existence of almost periodic solutions of a singularly perturbed differential equation with piecewise constant argument

Based on the investigation of almost periodic solutions to difference equations, the existence of almost periodic solution for a nonautonomous, singularly perturbed differential equation with piecewise constant argument is considered. In addition, the stability properties of these solutions are characterized by the construction of manifolds of initial data.     

About non-coincidence of invariant manifolds and intrinsic low dimensional manifolds (ILDM)

The present paper contains an analysis of some aspects of a well known method of Intrinsic Low-Dimensional Manifolds (ILDM), which is regularly used for model reduction purposes in a number of combustion problems. One of these aspects relates to an existence of additional solutions (so-called “ghost”-manifolds), which represent intrinsic low-dimensional manifolds and do NOT represent any slow invariant manifold even for two-dimensional singularly perturbed systems (for a small but finite singular parameter). These “ghost”-manifolds are examples that contradict to the conjecture about the coincidence of ILDM and slow invariant manifolds published previously. Another aspect of the ILDM-method concerns the so-called transition zones (turning manifolds) between different invariant manifolds. It is shown that transition manifolds can not be correctly described by the ILDM-method. This statement is illustrated by an example taken from the mathematical theory of combustion.     

On a singularly perturbed system of two second-order equations in the case of intersecting roots of the degenerate equation

For a singularly perturbed system of two second-order differential equations (one rapid and one slow), we prove the existence of a solution and obtain its asymptotics for the case in which the degenerate equation has two intersecting roots. In addition, we show that this solution is an asymptotically stable stationary solution of the corresponding parabolic problem and find its local attraction domain.     

一类含有小迟滞的奇摄动方程组的渐近解

本文研究了一类含有小迟滞的奇摄动方程组的渐近解.利用原问题的退化形式和伸长变量,依据边界层特有的性质,获得了边界层的渐近解.推广了奇摄动方程组初值问题和小迟滞问题的研究结果.     

Overstability: towards a global study

We consider singularly perturbed analytic differential equations in the complex domain with a turning point of order p and a p-dimensional control parameter a. We prove existence and exponential closeness of well behaved solutions under some geometric and transversality conditions. Furthermore, properties of formal solutions are studied and an application to “least term summation” is given.     

On qualitative properties of differential-algebraic equations

Linear systems of ordinary differential equations with identically degenerate coefficient matrix before the derivative of the unknown vector function are considered. The structure of general solutions and the notion of singular point of such systems are discussed. From the comparison of the properties of the “perturbed” and original problems, a sufficient criterion for the Lyapunov asymptotic stability of the zero solution is obtained.     

Asymptotics of the general solution to a linear singularly perturbed system of second-order differential equations with degeneracy

By using the perturbation methods and Newton diagrams, we study the structure and construct the asymptotics of the general solution to a linear singularly perturbed system of ordinary second-order differential equations in the case where the matrix by the higher derivative is degenerate.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 45, No. 4, pp. 561–575, April, 1993.     

Qualitative analysis of a singularly perturbed system in ℝ3

We present some qualitative analysis of a singularly perturbed system of ordinary differential equations with two slow variables and one fast variable. The study rests on the method of integral manifolds and its modification in connection with applied problems. The inspection of the system requires studying various types of oscillations. We propose some sufficient conditions for the existence of relaxation oscillations in this system in the case that the slow surface has two folds.     

Asymptotic Solutions of Systems of Linear Degenerate Integro-Differential Equations

We construct asymptotic solutions of a singularly perturbed system of integro-differential equations in which the matrix coefficient of the derivative is degenerate at a point.     

A Petrov-Galerkin mixed finite element method with exponential fitting

We discuss a Petrov-Galerkin mixed finite element formulation of the semiconductor continuity equations on a rectangular domain. We give error estimates for equations that are in principle degenerate in the singularly perturbed case. We give arguments that indicate that the method is also effective in the singularly perturbed case. We develop a discretization that gives a higher-order accurate solution for use in an a posteriori error estimator. © 1995 John Wiley & Sons, Inc.     

Integral manifolds of singularly perturbed systems of impulsive differential equations defined on tori

Sufficient conditions are obtained for the existence of integral manifolds of singularly perturbed systems of impulsive differential equations defined on tori, and some of their properties are investigated.

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Sunto Si presentano condizioni sufficienti a garantire l’esistenza di varietà integrali per sistemi, perturnati singolarmente, di equazioni differenziali impulsive su un toro. Si studiano inolte alcune loro proprietà.

     

Singularly perturbed boundary value problems with a power-law boundary layer

We consider boundary value problems for second-order singularly perturbed equations whose solution has a power-law boundary layer that occurs because the degenerate equation has multiple roots.     

A new fitted operator finite difference method to solve systems of evolutionary reaction-diffusion equations

Abstract

In recent years, fitted operator finite difference methods (FOFDMs) have been developed for numerous types of singularly perturbed ordinary differential equations. The construction of most of these methods differed though the final outcome remained similar. The most crucial aspect was how the difference operator was designed to approximate the differential operator in question. Very often the approaches for constructing these operators had limited scope in the sense that it was difficult to extend them to solve even simple one-dimensional singularly perturbed partial differential equations. However, in some of our most recent work, we have successfully designed a class of FOFDMs and extended them to solve singularly perturbed time-dependent partial differential equations. In this paper, we design and analyze a robust FOFDM to solve a system of coupled singularly perturbed parabolic reaction-diffusion equations. We use the backward Euler method for the semi-discretization in time. An FOFDM is then developed to solve the resulting set of boundary value problems. The proposed method is analyzed for convergence. Our method is uniformly convergent with order one and two, respectively, in time and space, with respect to the perturbation parameters. Some numerical experiments supporting the theoretical investigations are also presented.     

Exact slow-fast decomposition of the singularly perturbed matrix differential Riccati equation

In this paper the Hamiltonian matrix formulation of the Riccati equation is used to derive the reduced-order pure-slow and pure-fast matrix differential Riccati equations of singularly perturbed systems. These pure-slow and pure-fast matrix differential Riccati equations are obtained by decoupling the singularly perturbed matrix differential Riccati equation of dimension n₁+n₂ into the pure-slow regular matrix differential Riccati equation of dimension n₁ and the pure-fast stiff matrix differential Riccati equation of dimension n₂. A formula is derived that produces the solution of the original singularly perturbed matrix differential Riccati equation in terms of solutions of the pure-slow and pure-fast reduced-order matrix differential Riccati equations and solutions of two reduced-order initial value problems. In addition to its theoretical importance, the main result of this paper can also be used to implement optimal filtering and control schemes for singularly perturbed linear time-invariant systems independently in pure-slow and pure-fast time scales.     

On the Existence of Pulses in Reaction- Diffusion- Equations

We apply the theory of invariant manifolds for singularly perturbed ordinary differential equations and results about the persistence of homoclinic orbits in autonomous differential systems with several parameters in order to establish the existence of pulses in reaction-diffusion systems. Essential assumptions for the existence of pulses are the following: (i) Existence of a homoclinic orbit to a hyperbolic equilibrium in the corresponding reaction system. (ii) The quotient of some measure for the diffusivities and the square of the puls speed is sufficiently small. (iii) Validity of some transversality condition. The last assumption requires the occurence of parameters in the reaction term.     

Multifrequency oscillations of singularly perturbed systems

We consider a system of differential equations that consists of two parts, a regularly perturbed and a singularly perturbed one. We assume that the matrix of the linear part of the regularly perturbed system has pure imaginary eigenvalues, while the matrix of the singularly perturbed part is hyperbolic; i.e., all of its eigenvalues have nonzero real parts.     

The exponential asymptotic stability of singularly perturbed delay differential equations with a bounded lag

This paper is concerned with the exponential stability of singularly perturbed delay differential equations with a bounded (state-independent) lag. A generalized Halanay inequality is derived in Section 2, and in Section 3 a sufficient condition will be provided to ensure that any solution of the singularly perturbed delay differential equations (DDEs) with a bounded lag is exponentially stable uniformly for sufficiently small ε>0. This type of exponential asymptotic stability can obviously be applied to general delay differential equations with a bounded lag.     

Some Fredholm equations with boundary layer resonance

Certain singularly perturbed differential equations which exhibit boundary layer resonance are difficult to solve by the application of standard asymptotic methods. After reformulation as a singularly perturbed integral equation and treatment by a recently developed asymptotic methodology, the desired solution is obtained in a straightforward manner.