Product integrals II: Contour integrals

This paper continues the joint work of the authors begun in the article “On Strong Product Integration” [J. Functional Analysis, submitted]. We consider product integrals along contours; the point of view and development is analogous to the usual complex variable theory of ordinary contour integrals. Our main results are Theorem 2.3 (homotopy invariance of product integrals, an analog of Cauchy's integral theorem) and Theorem 3.4 (an analog of Cauchy's integral formula or the residue theorem).     

Hurwitz' theorem implies Rouché's theorem

It is well known that Hurwitz's theorem is easily proved from Rouché's theorem. We show that conversely, Rouché's theorem is readily proved from Hurwitz' theorem. Since Hurwitz' theorem is easily proved from the formula giving the number of roots of an analytic function, our result thus gives also a simple proof of Rouché's theorem.     

四元数分析中k-左正则函数的性质及其Riemann边值问题

讨论了四元数分析中k-左正则函数的若干函数论性质,如Cauchy-Pompeiu公式,Cauchy公式,k-左正则函数的表示,Plemelj公式等.同时考虑了k-左正则函数的Riemann边值问题,通过k-左正则函数的Plemelj公式,将问题转化为奇异积分方程组,再利用积分方程理论和压缩映像原理证明了该问题解的存在唯一性.     

On Some Integral Transformations and Their Application to the Solution of Boundary-Value Problems in Mathematical Physics

We obtain a formula for the expansion of an arbitrary function in a series in the eigenfunctions of the Sturm–Liouville boundary-value problem for the differential equation of cone functions. On the basis of this result, we derive a series of integral transformations (including well-known ones) and inversion formulas for them. We apply these formulas to the solution of initial boundary-value problems in the theory of heat conduction for circular hollow cones truncated by spherical surfaces.     

On a theorem of Hermite and Hurwitz

The Hermite-Hurwitz theorem computes the degree, over $\text{R}$, of a real rational function ? in terms of the signature of an associated quadratic form—known today as the Hankel matrix of ?. This formula, which Hermite was led to by his work on the problem of representing integers as sums of squares, gave rise to striking applications in the theory of equations and in the stability theory of ordinary differential equations. In this paper, this theorem and various generalizations to the matrix-valued case are discussed and described in terms of signature formulae. These include its relation to stability theory and the matrix Hermite-Hurwitz theorem of Bitmead-Anderson as applied to questions of circuit synthesis. This also includes a global form of Hörmander's signature formula for the Maslov index of a rational loop in a Lagrangian Grassmannian, due to Byrnes and Duncan, and applications to the topology of spaces of rational matrix-valued functions, following the work of Brockett, Byrnes, and Duncan. This includes, in particular, a topological proof of the matrix Hermite-Hurwitz theorem.     

Interval vortex methods

By means of the integral version of vortex equation, the technique of Green's function, and the vorticity‐to‐velocity map, a new kind of interval methods for solving the initial‐periodic boundary value problem of two‐dimensional incompressible Navier–Stokes equation is introduced, which consists of both an approximate scheme and a set of pointwise intervals covering the exact solution. The convergence theorem corresponding to the scheme is proved, and the order of error width for the two‐sided bounds is also considered. Finally, a simple numerical example illustrates our corroboration. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 30: 1368–1396, 2014     

Scattering of sound from point sources by multiple circular cylinders using addition theorem and superposition technique

In this study, we use the addition theorem and superposition technique to solve the scattering problem with multiple circular cylinders arising from point sound sources. Using the superposition technique, the problem can be decomposed into two individual parts. One is the free‐space fundamental solution. The other is a typical boundary value problem (BVP) with specified boundary conditions derived from the addition theorem by translating the fundamental solution. Following the success of null‐field boundary integral formulation to solve the typical BVP of the Helmholtz equation with Fourier densities, the second‐part solution is easily obtained after collocating the observation point exactly on the real boundary and matching the boundary condition. The total solution is obtained by superimposing the two parts which are the fundamental solution and the semianalytical solution of the Helmholtz problem. An example was demonstrated to validate the present approach. The parameter study of size and spacing between cylinders are addressed. The results are well compared with the available theoretical solutions and experimental data. © 2011 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2011     

A NEW INTEGRAL TRANSFORM AND ITS APPLICATIONS

In the present paper,the authors introduce a new integral transform which yields a number of potentially useful(known or new) integral transfoms as its special cases.Many fundamental results about this new integral transform,which are established in this paper,include(for example) existence theorem,Parseval-type relationship and inversion formula.The relationship between the new integral transform with the H-function and the H-transform are characterized by means of some integral identities.The introduced transform is also used to find solution to a certain differential equation.Some illustrative examples are also given.     

Quadrature formulas for the Laplace and Mellin transforms

A discrete Laplace transform and its inversion formula are obtained by using a quadrature of the integral Fourier transform which is given in terms of Hermite polynomials and its zeros. This approach yields a convergent discrete formula for the two-sided Laplace transform if the function to be transformed falls off rapidly to zero and satisfies given conditions of integrability, achieving convergence also for singular functions. The inversion formula becomes a quadrature formula for the Bromwich integral. The use of asymptotic formulae yields an algorithm to compute the discrete Laplace transform by using only exponentials.     

Liénard方程极限环的存在唯一性定理

<正> 的极限环的存在唯一性问题[1,2],给出了定理1,此定理的一个推论即已包含了熟知的Lienard定理以及Levinson-Smith[3],Sansone[2],Barbalat[4],余澍祥[5]的存在唯一性定理.作为定理1推论的直接应用,还对方程     

A Banach algebra of Feynman integrable functionals with application to an integral equation formally equivalent to Schroedinger's equation

A Banach algebra A of functionals on C[a, b] is introduced and it is proved that the operator-valued Feynman integral recently defined by Cameron and Storvick exists for functionals in A. Two existence theorems of Cameron and Storvick are seen to be special cases of this result; in fact, even in these cases, the present theorem gives improved results.Cameron and Storvick have used their function space integral to give a solution to an integral equation formally equivalent to Schroedinger's equation; using our existence theorem, we give a relatively brief and transparent proof of this result.     

New formulae for higher order derivatives and applications

We present new formulae (the Slevinsky–Safouhi formulae I and II) for the analytical development of higher order derivatives. These formulae, which are analytic and exact, represent the kth derivative as a discrete sum of only k+1 terms. Involved in the expression for the kth derivative are coefficients of the terms in the summation. These coefficients can be computed recursively and they are not subject to any computational instability. As examples of applications, we develop higher order derivatives of Legendre functions, Chebyshev polynomials of the first kind, Hermite functions and Bessel functions. We also show the general classes of functions to which our new formula is applicable and show how our formula can be applied to certain classes of differential equations. We also presented an application of the formulae of higher order derivatives combined with extrapolation methods in the numerical integration of spherical Bessel integral functions.     

The analytic continuation of solutions to elliptic boundary value problems in two independent variables

An explicit representation is derived for the continuation across an analytic boundary of the solution to a boundary value problem for an analytic elliptic equation of second order in two independent variables. The representation is in terms of Cauchy data on the boundary and the complex Riemann function. This is equivalent to a representation for the solution to Cauchy's problem given by Henrici in 1957. It is confirmed that the method of complex characteristics is satisfactory for locating real singularities in the solution provided that the Riemann function is entire in its four arguments. Applications to Laplace's and Helmholtz's equations are discussed. By inserting known, simple solutions to the latter equation into the representation formula, several nontrivial integral relations involving the Bessel function J₀, and a possibly new series expansion for J_μ(x), are found.     

The Lagrange inversion theorem in the smooth case

The classical Lagrange inversion theorem is a concrete, explicit form of the implicit function theorem for real analytic functions. An explicit construction shows that the formula is not true for all merely smooth functions. The authors modify the Lagrange formula by replacing the smooth function by its Maclaurin polynomials. The resulting modified Lagrange series is, in analogy to the Maclaurin polynomials, an approximation to the solution function accurate to o(x^N) as x→0.     

Clifford分析中广义超正则函数的一个非线性边值问题

讨论了Cliffrd分析中广义超正则函数的一个非线性边值问题.首先将广义超正则函数分解为两个奇异积分算子,然后给出了广义超正则函数的Plemelj公式及相关奇异积分算子的性质,最后利用Schauder不动点原理证明了广义超正则函数的一个非线性边值问题的解的存在性及积分表达式.     

On the extension of von Neumann-Aumann's theorem

We give a measurable selection theorem which generalizes von Neumann-Aumann's theorem when the domain of definition is an abstract measurable space and the range space is a Suslin space.As application we give a measurable implicit function theorem and a parametrized version of Choquet's theorem on integral representation.     

Parametric integro-interpolational method of solution of singular integral equations

Use of a parametric intego-interpolational method is proposed for the study of singular integral equations with a singular kernel of Cauchy type; the method involves replacing the regular part of a quadratic formula with subsequent inversion of a singular integral. Justification is given for the computational scheme employed as well as for an estimate of the rate of convergence of the approximate solution, obtained with its aid, to the exact solution.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 44, No. 11, pp. 1614–1617, November, 1992.     

The Sampling Theorem and Several Equivalent Results in Analysis

First we show that several fundamental results on functions from theBernstein spaces (such as Bernstein's inequality andthe reproducing formula) can be deduced from a weak form of the classicalsampling theorem. In §3 we discuss the mutual equivalence of thesampling theorem, the derivative sampling theorem and a harmonic functionsampling theorem. In §§4–6 we discuss connections between thesampling theorem and various important results in complex analysis andFourier analysis. Our considerations include Cauchy's integral formula,Poisson's summation formula, a Gaussian integral, certain properties ofweighted Hermite polynomials, Plancherel's theorem, the maximum modulusprinciple, and the Phragmén–Lindelöf principle.     

Generalized reflected BSDEs driven by a Lévy process and an obstacle problem for PDIEs with a nonlinear Neumann boundary condition

In this paper, we derive the existence and uniqueness of the solution for a class of generalized reflected backward stochastic differential equations (GRBSDEs in short) driven by a Lévy process, which involve the integral with respect to a continuous process by means of the Snell envelope, the penalization method and the fixed point theorem. In addition, we obtain the comparison theorem for the solutions of the GRBSDEs. As an application, we give a probabilistic formula for the viscosity solution of an obstacle problem for a class of partial differential-integral equations (PDIEs in short) with a nonlinear Neumann boundary condition.     

Weighted inversion numbers,restricted growth functions,and standard young tableaux

We give a family of weighted inversion numbers with the same generating function which interpolate between the inversion number and MacMahon's major index. Foata's bijection is obtained in a natural way from a simple involution. An alternative proof uses q-difference equations which yield some new results. We obtain a new generating function for restricted growth functions and two q-analogs of a formula for the number of standard Young tableaux of a given shape. While the first really goes back to MacMahon, the second uses one of our weighted inversion numbers and appears to be new.