Volterra integral equations and evolution equations with an integral condition

We suggest a simple method for reducing problems with an integral condition for evolution equations to a Volterra integral equation of the first kind. For Volterra equations of the convolution type, we indicate necessary and sufficient solvability conditions for the case in which the right-hand side lies in some classes of functions of finite smoothness. We use these conditions to construct examples of nonexistence of a local solution for the heat equation with an integral condition.     

Triple and quadruple integral equations occurring in diffraction theory

A formal scheme has been set up to solve the triple and quadruple integral equations of certain type which occur in diffraction theory. The operational theory has been employed in the analysis and equations have been reduced to the solution of simultaneous Fredholm equations.     

A trigonometric Galerkin method for volume integral equations arising in TM grating scattering

Transverse magnetic (TM) scattering of an electromagnetic wave from a periodic dielectric diffraction grating can mathematically be described by a volume integral equation.This volume integral equation, however, in general fails to feature a weakly singular integral operator. Nevertheless, after a suitable periodization, the involved integral operator can be efficiently evaluated on trigonometric polynomials using the fast Fourier transform (FFT) and iterative methods can be used to solve the integral equation. Using Fredholm theory, we prove that a trigonometric Galerkin discretization applied to the periodized integral equation converges with optimal order to the solution of the scattering problem. The main advantage of this FFT-based discretization scheme is that the resulting numerical method is particularly easy to implement, avoiding for instance the need to evaluate quasiperiodic Green’s functions.     

Weakly singular integral equations with operator-valued kernels and an application to radiation transfer problems

The standard problem of radiation transfer in a bounded regionG ⁿ can be reformulated as a weakly singular integral equation with an unknown functionu: GC(S ^n–1) and a kernelK: ((G × G }x=y}, which is continuously differentiable with respect to the operator strong convergence topology. We take these observations into the basis of an abstract treatment of weakly singular integral equations with (E)-valued kernels, whereE is a Banach space. Our purpose is to characterize the smoothness of the solution by proving that it belongs to special weighted spaces of smooth functions. On the way, realizing the proof techniques, we establish the compactness of the integral operator or its square inL _p (G,E),BC(G,E), and other spaces of interest in numerical analysis as well as in weighted spaces of smooth functions. The smoothness results are specified for the standard problem of radiation transfer as well as for the corresponding eigenvalue problem.     

A generalized integral with applications to trigonometric series

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The authors wish to thank the referee whose comments improved the presentation of the paper. In fact, the present form of Lemma 2, which was originally very long, is due to the referee.     

Rational approximations of trigonometric matrices with application to second-order systems of differential equations

We consider the direct treatment of the second-order system of equations y” (t)+ Ay(t) = tf;(t), such as might arise in finite-element or finite-difference semidiscretizations of the wave equation. We develop the exact solution and some three-term recurrences involving trigonometric matrices. We approximate these trigonometric matrices by rational approximants of Padé type and thus develop a two-parameter family of approximation schemes. We analyze the stability behavior and computational complexity of members of this family and isolate four schemes for numerical experimentation, the results of which we tabulate. We single out as particularly effective the classical Stormer-Numerov method and also a new sixth-order scheme.     

Identities for trigonometric B-splines with an application to curve design

In this paper we investigate some properties of trigonometric B-splines. We establish a complex integral representation for these functions, which is in certain analogy to the polynomial case, but the proof of which has to be done in a different and more complicated way. Using this integral representation, we can prove some identities concerning the evaluation of a trigonometric B-spline, its derivative and its partial derivative w.r.t. the knots. Finally we show that—in the case of equidistant knots—the trigonometric B-splines of odd order form a partition of a constant, and therefore the corresponding B-spline curve possesses the convex-hull property. This is illustrated by a numerical example.     

A new interpretation of Cauchy type singular integrals with an application to singular integral equations

Cauchy type integrals were given the interpretation of the principal value for points inside the integration interval. Here this interpretation is modified and generalized in a very simple manner. The new interpretation in general is not equivalent to the classical one. The relationship between the new interpretation and the classical one is investigated and various applications of the new interpretation (to the Plemelj formulas, the Riemann-Hilbert boundary value problem, singular integral equations, the inversion formula, quadrature rules and interface crack problems) are presented.     

On oscillatory integral Hilbert transformation with trigonometric polynomial phase

Let $ \mathcal{P}_n $ denote the set of algebraic polynomials of degree n with the real coefficients. Stein and Wpainger [1] proved that $$ \mathop {\sup }\limits_{p( \cdot ) \in \mathcal{P}_n } \left| {p.v.\int_\mathbb{R} {\frac{{e^{ip(x)} }} {x}dx} } \right| \leqslant C_n , $$ where C _n depends only on n. Later A. Carbery, S. Wainger and J. Wright (according to a communication obtained from I. R. Parissis), and Parissis [3] obtained the following sharp order estimate $$ \mathop {\sup }\limits_{p( \cdot ) \in \mathcal{P}_n } \left| {p.v.\int_\mathbb{R} {\frac{{e^{ip(x)} }} {x}dx} } \right| \sim \ln n. $$ . Now let $ \mathcal{T}_n $ denote the set of trigonometric polynomials $$ t(x) = \frac{{a_0 }} {2} + \sum\limits_{k = 1}^n {(a_k coskx + b_k sinkx)} $$ with real coefficients a _k , b _k . The main result of the paper is that $$ \mathop {\sup }\limits_{t( \cdot ) \in \mathcal{T}_n } \left| {p.v.\int_\mathbb{R} {\frac{{e^{it(x)} }} {x}dx} } \right| \leqslant C_n , $$ with an effective bound on C _n . Besides, an analog of a lemma, due to I. M. Vinogradov, is established, concerning the estimate of the measure of the set, where a polynomial is small, via the coefficients of the polynomial.     

Uniqueness theorem for integral equations and its application

This paper is devoted to answering a question asked recently by Y. Li regarding geometrically interesting integral equations. The main result is to give a necessary and sufficient condition on the parameters so that the integral equation with parameters to be discussed in this paper have regular solutions. In the case such condition is satisfied, we will write down the exact solution. As its application of our method, we should show that the non-existence theory of the solutions of prescribed scalar curvature equation on Sn can be generalized to that of prescribed Branson-Paneitz Q-curvature equations on Sn.     

Sharp inequalities for trigonometric polynomials with respect to integral functionals

The problem on sharp inequalities for linear operators on the set of trigonometric polynomials with respect to integral functionals \(\int_0^{2\pi } {\phi \left( {\left| {f\left( x \right)} \right|} \right)dx}\) is discussed. A solution of the problem on trigonometric polynomials with given leading harmonic of least deviation from zero with respect to such functionals over the set of all functions φ defined, nonnegative, and nondecreasing on the semiaxis [0,+∞) is given.     

Existence and uniqueness of traveling waves for non-monotone integral equations with application

This paper is concerned with the traveling waves in a class of non-monotone integral equations. First we establish the existence of traveling waves. The approach is based on the construction of two associated auxiliary monotone integral equations and a profile set in a suitable Banach space. Then we show that the traveling waves are unique up to translations under some reasonable assumptions. The exact asymptotic behavior of the profiles as ξ→−∞ and the existence of minimal wave speed are also obtained. Finally, we apply our results to an epidemic model with non-monotone “force of infection”.     

Spectral singularities of Klein-Gordon s-wave equations with an integral boundary condition

We investigate the spectral singularities and the eigenvalues of the boundary value problem $$\begin{gathered} y'' + \left[ {\lambda - Q\left( x \right)} \right]^2 y = 0,x \in R_ + = [0,\infty ), \hfill \\ \quad \int\limits_0^\infty {K\left( x \right)y\left( x \right)dx + \alpha y'\left( 0 \right) - \beta y\left( 0 \right) = 0,} \hfill \\ \end{gathered}$$ where Q and K are complex valued functions, K∈L ²(R ₊), α,β∈C with |α|+|β|≠0 and λ is a spectral parameter.     

Solutions of some Fredholm integral equations using fractional integration,with an application to a forced convection problem

It is shown that certain Fredhom integral equations of the first kind can be written in terms of fractional integrals. The inversion of these operators, and thus the solutions of the integral equations, can than be deduced from well known properties of fractional integrals. The particular cases studied involve equations arising in heat transfer, viscous flow, and elastic half-space problems.The equations may be solved in terms of classically integrable functions or in a generalised function space. In the latter case the solutions are not unique but the most general solution of the equations is constructed. In the course of this analysis a uniqueness theorem for the classical cases is derived as a by-product.A relationship between certain special functions which enables series solutions to be obtained is shown to be valid in the generalised function space after suitably modifying certain definitions and identities.

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Zusammenfassung Es wird gezeigt, dass gewisse Fredholmsche Integralgleichungen erster Art als Integrale gebrochener Ordnung dargestellt werden können. Die Umkehrung dieser Operatoren, und somit die Auflösung der Integralgleichungen, kann dann mittels bekannter Eigenschaften der Integrale gebrochener Ordnung erfolgen. Bei den hier untersuchten Fällen handelt es sich um Gleichungen, die bei Aufgaben der Wärmeleitung bei zähen Flüssigkeiten und bei elastischen Halbräumen auftreten.Die Gleichungen können entweder durch im klassischen Sinne integrierbare Funktionen oder in einem verallgemeinerten Funktionenraum aufgelöst werden. Im letzteren Fall sind die Lösungen nicht eindeutig; die allgemeinste Form der Lösung wird jedoch angegeben. Als Nebenprodukt der Untersuchung ergibt sich ein Eindeutigkeitssatz für den klassischen Fall.Eine Beziehung zwischen gewissen speziellen Funktionen, welche Reihendarstellungen der Lösungen ermöglicht, erweist sich nach Modifikation gewisser Definitionen und Identitäten als auch im verallgemeinerten Funktionenraum gültig.