A Liapunov functional for a matrix neutral difference-differential equation with one delay

For the matrix neutral difference-differential equation $\text{x}\text{?}\text{(t) + A}\text{x}\text{?}\text{(t ? τ)  Bx(t) + Cx(t ? τ)}$ we construct a quadratic Liapunov functional which gives necessary and sufficient conditions for the asymptotic stability of the solutions of that equation. We consider a difference equation approximation of the difference-differential equation, and for this difference equation we construct a Liapunov function from which we obtain the desired Liapunov functional by an appropriate limiting process. The Liapunov functional thus obtained gives the best possible estimate for the rates of growth or decay of the solutions of the matrix neutral difference-differential equation. The results obtained are natural generalizations of previous results obtained for a matrix retarded difference-differential equation with one delay.     

A Liapunov functional for a singular integral equation

We consider a scalar integral equation where a∈L²[0,∞), while C(t,s) has a significant singularity, but is convex when t−s>0. We construct a Liapunov functional and show that g(t,x(t))−a(t)∈L²[0,∞) and that x(t)−a(t)→0 pointwise as t→∞. Small perturbations are also added to the kernel. In addition, we consider both infinite and finite delay problems. This paper offers a first step toward treating discontinuous kernels with Liapunov functionals.     

First mixed problem for a parabolic difference-differential equation

The first mixed boundary value problem for a parabolic difference-differential equation with shifts with respect to the spatial variables is considered. The unique solvability of this problem and the smoothness of generalized solutions in some cylindrical subdomains are established. It is shown that the smoothness of generalized solutions can be violated on the interfaces of neighboring subdomains. Translated fromMatematicheskie Zametki, Vol. 66, No. 1, pp. 145–153, July, 1999.     

Note on a versatile Liapunov functional: applicability to an elliptic equation

A novel, very effective Liapunov functional was used in previous papers to derive decay and asymptotic stability estimates (with respect to time) in a variety of thermal and thermo‐mechanical contexts. The purpose of this note is to show that the versatility of this functional extends to certain non‐linear elliptic boundary value problems in a right cylinder, the axial co‐ordinate in this context replacing the time variable in the previous one. A steady‐state temperature problem is considered with Dirichlet boundary conditions, the condition on the boundary being independent of the axial co‐ordinate. The functional is used to obtain an estimate of the error committed in approximating the temperature field by the two‐dimensional field induced by the boundary condition on the lateral surface. Copyright © 2002 John Wiley & Sons, Ltd.     

Boundary value problem for a mixed-type equation with a difference-differential operator

The Tricomi problem for a mixed-type equation with retarded argument in an unbounded domain is considered. The unique solvability of the problem is proved without restrictions on the delay magnitude. The existence of a solution follows from the solvability of a difference equation. Closed-form integral representations for the solutions are derived.     

Wilson's functional equation for vector and matrix functions

We determine the general solution of the functional equation

where is a 2-divisible abelian group, is a vector-valued function and is a matrix-valued function. Using this result we solve the scalar equation

which contains as special cases, among others, the d'Alembert and Wilson equations and the parallelogram law.

     

A new inversion-free method for a rational matrix equation

Motivated by the classical Newton-Schulz method for finding the inverse of a nonsingular matrix, we develop a new inversion-free method for obtaining the minimal Hermitian positive definite solution of the matrix rational equation X+A^∗X^-1A=I, where I is the identity matrix and A is a given nonsingular matrix. We present convergence results and discuss stability properties when the method starts from the available matrix AA^∗. We also present numerical results to compare our proposal with some previously developed inversion-free techniques for solving the same rational matrix equation.     

A matrix equation for association schemes

Let be a self-dual P-polynomial association scheme. Then there are at most 12 diagonal matricesT such that (PT)³ =I. Moreover, all of the solutions for the classical infinite families of such schemes (including the Hamming scheme) are classified.This work was supported by NSF grant DMS-9400510.     

A difference-differential analogue of the burgers equation: Stability of the two-wave behavior

We study the Cauchy problem for the difference-differential equation

A nonlinear boundary problem for a functional differential equation

The abstract nonlinear boundary value problem , is treated. Existence and uniqueness results are obtained.     

On matrix measures and convex Liapunov functions

In this paper, we extend the concept of the measure of a matrix to encompass a measure induced by an arbitrary convex positive definite function. It is shown that this “modified” matrix measure has most of the properties of the usual matrix measure, and that many of the known applications of the usual matrix measure can therefore be carried over to the modified matrix measure. These applications include deriving conditions for a mapping to be a diffeomorphism on Rⁿ, and estimating the solution errors that result when a nonlinear network is approximated by a piecewise linear network. We also develop a connection between matrix measures and Liapunov functions. Specifically, we show that if V is a convex positive definite function and A is a Hurwitz matrix, then μ_V(A) < 0, if and only if V is a Liapunov function for the system $\text{x}\text{?}\text{= Ax}$. This linking up between matrix measures and Liapunov functions leads to some results on the existence of a “common” matrix measure μ_V(·) such that μ_V(A_i) < 0 for each of a given set of matrices A₁,…, A_m. Finally, we also give some results for matrices with nonnegative off-diagonal terms.     

A functional equation

The translational functional equation (1) with right-hand side analytic in a finite convex region D is investigated. It is proved that a solution exists which is analytic in a finite convex region G₁ determined by G. A corollary of this result is the existence of analytic solutions of differential-difference equations of finite order and of difference equations of infinite order with constant coefficients.Translated from Matematicheskie Zametki, Vol. 5, No. 6, pp. 733–742, June, 1969.     

A linear matrix equation: a criterion for block similarity

In this paper we study a homogeneous linear matrix equation related to the block similarity of rectangular matrices. We obtain the dimension of the vector space of its solutions and we describe these solutions. We give a characterization of the block similarity by rank tests. We extend Roth's criterion to the corresponding non homogeneous equation.     

A functional equation

Existence theorems for and the determination of continuous solutions, defined on the real axis R, of the functional equationf (t)=A[t,f (at–b),f (at–c)], wherea, b, and c are real parameters, A:R×E×E E is a continuous operator, and E is a Banach space.Translated from Matematicheskie Zametki, Vol. 9, No. 2, pp. 161–170, February, 1971.The author wishes to thank B. N. Sadovskii for his interest and help in this work.