A problem with the Frankl and Bitsadze-Samarskii condition on the line of degeneracy and on parallel characteristics for a mixed-type equation

In this paper we study the boundary-value problem with the Frankl and Bitsadze-Samarskii condition on the line of degeneracy and on parallel characteristics for a mixed-type equation with a singular coefficient. We prove the existence of a solution by the method of integral equations, and we do its uniqueness with the help of the extremum principle.     

On the Dirichlet-type problem for elliptic systems degenerate at a line

In this paper, the Dirichlet-type problem for the system of elliptic equations of second order with the degeneracy at a line crossing the domain is considered. The Dirichlet-type problem with additionally given asymptotics of the solution at this line is discussed. The uniqueness and the existence of the solution of this problem in the class of Hölder functions is proved.     

The Tricomi problem for second order linear equations of mixed type with parabolic degeneracy

In Bers, 1958, Mathematical Aspects of Subsonic and Transonic Gas Dynamics (New York: Wiley); Bitsadze, 1988, Some Classes of Partial Differential Equations (New York: Gordon and Breach); Rassias, 1990, Lecture Notes on Mixed Type Partial Differential Equations (Singapore: World Scientific); Salakhitdinov and Islomov, 1987, The Tricomi problem for the general linear equation of mixed type with a nonsmooth line of degeneracy. Soviet Math. Dokl., 34, 133–136; Smirnov, 1978, Equations of Mixed type (Providence, RI: American Mathematical Society), the authors posed and discussed the Tricomi problem of second order equations of mixed type with parabolic degeneracy, which possesses important application to gas dynamics. The present article deals with the Tricomi problem for general second order equations of mixed type with parabolic degeneracy. Firstly the formulation of the problem for the equations is given, next the representations and estimates of solutions for the above problem are obtained, finally the existence of solutions for the problem is proved by the successive iteration and the method of parameter extension. In this article, we use the complex method, namely the complex functions in the elliptic domain and the hyperbolic complex functions in hyperbolic domain are used (see Wen, 2002, Linear and Quasilinear Equations of Hyperbolic and Mixed Types (London: Taylor and Francis)).     

退化约束的既约变尺度法

既约梯度法是求解线性等式与变量非负约束的非线性规划问题的有效方法,它的优点是降低问题的维数.变尺度方法是求解无约束优化问题的快速方法.文[1]将上述两种方法结合起来,给出了约束非退化并采用精确一维搜索的既约变尺度法,并证明了算法的收敛性与超线性收敛速度.但从计算的实现上来说,必须考虑使用非精确搜索的算法.为了使算法的适应范围更加广泛,也需要放弃约束非退化的假设.本文在满足上述两个要求下给出了退化约束条件下并采用非精确一维搜索的既约变尺度法,证明了算法的全局收敛性与超线性的收敛速度.     

Asymptotic Behavior of Solutions to a Class of Semilinear Parabolic Equations with Boundary Degeneracy

This paper concerns the asymptotic behavior of solutions to one-dimensional semilinear parabolic equations with boundary degeneracy both in bounded and unbounded intervals. For the problem in a bounded interval, it is shown that there exist both nontrivial global solutions for small initial data and blowing-up solutions for large one if the degeneracy is not strong. Whereas in the case that the degeneracy is strong enough, the nontrivial solution must blow up in a finite time. For the problem in an unbounded interval, blowing-up theorems of Fujita type are established. It is shown that the critical Fujita exponent depends on the degeneracy of the equation and the asymptotic behavior of the diffusion coefficient at infinity, and it may be equal to one or infinity. Furthermore, the critical case is proved to belong to the blowing-up case.     

Regularity for p-harmonic equations with right-hand side in Orlicz-Zygmund classes

We establish regularity results for solutions of some degenerate elliptic PDEs, with right-hand side in a suitable Orlicz-Zygmund class. The nonnegative function which measures the degree of degeneracy of the ellipticity bounds is assumed to be exponentially integrable. We find that the scale of improved regularity is logarithmic and we indicate its exact dependence on the degree of the degeneracy of the problem.     

The Dirichlet Problem for a Hyperboli-Type Equation with Power Degeneracy in a Rectangular Domain

The first boundary value problem is studied for a linear hyperbolic equation in a rectangle with a power degeneracy on one of its sides for different degrees of degeneracy. A uniqueness criterion is established. The solution is constructed as the sum of a Fourier series. The problem of small denominators arises when justifying the convergence of this series. In this connection, some estimates for the separation of the small denominators from zero are established with the corresponding asymptotics specified. It is these asymptotics that have made it possible to substantiate the existence of a regular problem solution.     

Cauchy Problem for Nonuniformly Parabolic Equations with Degeneracy

In spaces of classical functions with power weight, we prove the existence and uniqueness of a solution of the Cauchy problem for nonuniformly parabolic equations without restrictions on the power order of degeneracy of the coefficients. We obtain an estimate for the solution of the problem in the corresponding spaces.     

Degeneration and regularization of the operator in the Cauchy problem for the Schrödinger equation

The Cauchy problem for the Schrödinger equation whose operator degenerates on a half-line is studied. In order to approximate a solution to the problem with degeneracy by solutions to well-posed problems, the notion of regularization for an operator with degeneracy is introduced; an approximative solution to a problem with degeneracy is defined as the limit of a sequence of regularized problems. The dependence of the approximative solution on the choice of the class of admissible regularizations is studied. The weak compactness of sequences of states determined by sequences of solutions to regularized problems in the topologies determined by the space of all bounded linear operators and by subspaces of mutually commuting bounded linear operators is investigated.     

A nonlocal boundary-value problem with conormal derivative for a mixed-type equation with two inner degeneration lines and various orders of degeneracy

We prove the unique solvability of the boundary value problem with conormal derivative for a mixed-type equation with two inner degeneration lines and with various orders of degeneracy.     

On Localization of Solutions of Elliptic Equations with Nonhomogeneous Anisotropic Degeneracy

The work deals with the Dirichlet problem for elliptic equations with nonhomogeneous anisotropic degeneracy in a possibly unbounded domain of multidimensional Euclidean space. The existence of weak solutions is proved. Some conditions are established connecting the character of nonlinearity of the equation and the geometric characteristics of the domain which guarantee the one-dimensional localization (vanishing) of weak solutions. The equation with anisotropic degeneracy is shown to admit localized solutions even in the absence of absorption.     

The Exterior Tricomi Problem for Generalized Mixed Equations with Parabolic Degeneracy

This paper deals with the exterior Tricomi problem for generalized mixed equations with parabolic degeneracy. Firstly the representation of solutions of the problem for the equations is given, and then the uniqueness and existence of solutions are proved by a new method.     

On Determining Sources with Compact Supports in a Bounded Plane Domain for the Heat Equation

The inverse problem of determining the source for the heat equation in a bounded domain on the plane is studied. The trace of the solution of the direct problem on two straight line segments inside the domain is given as overdetermination (i.e., additional information on the solution of the direct problem). A Fredholm alternative theorem for this problem is proved, and sufficient conditions for its unique solvability are obtained. The inverse problem is considered in classes of smooth functions whose derivatives satisfy the Hölder condition.     

THE DEGENERACY PROBLEM OF TWO-DIMENSIONAL LINEAR RECURRING ARRAYS

The degeneracy degree and degeneracy position sets of a wo-dimensional linear recurrence relation set are characterized. The fact that a linear recurring array is essentially a doubly periodic array is shown. By using the Grbner base theory, a calculation formula for degeneracy degree is given and the existence of a special degeneracy position set is proved. In the present paper, the degeneracy problem of the two-dimensional linear recurring arrays is completely solved.     

Boundary value problem for a class of degenerate quasilinear parabolic equations with singularity

This paper is concerned with a class of quasilinear parabolic equations with singularity and arbitrary degeneracy. The existence and uniqueness of generalized solutions to a kind of boundary value problem is established.     

Degeneracy graphs: theory and application an updated survey

A survey of various aspects of the theory and application of degeneracy graphs (DGs for short) is given. The notion and some basic properties of DGs are introduced, cycling of the simplex method is discussed, the neighborhood problem is tackled, and the application of the so-called optimum DGs to particular problems which are connected with optimal degenerate solutions of a linear programming problem is presented. The impact of weakly redundant constraints on various postoptimal analyses under degeneracy is briefly described.     

The inverse problem with free boundary for a weakly degenerate parabolic equation

In a domain with free boundary, we consider the inverse problem of determination of a time-dependent coefficient of the first derivative of the unknown function in a parabolic equation with weak power degeneracy. The integral conditions are given as overdetermination conditions. The conditions of existence and uniqueness of the classical solution to this problem are established.     

Cauchy Problem for a Quasi-Linear Hyperbolic Equation with Closed Support of Data

The Cauchy problem with closed support for a quasi-linear hyperbolic equation with a possible parabolic degeneracy is studied. The structure of the domain of solution is studied and initial conditions for which there exist areas of impenetrability of waves are found.     

Dealing with degeneracy in reduced gradient algorithms

Many algorithms for linearly constrained optimization problems proceed by solving a sequence of subproblems. In these subproblems, the number of variables is implicitly reduced by using the linear constraints to express certain ‘basic’ variables in terms of other variables. Difficulties may arise, however, if degeneracy is present; that is, if one or more basic variables are at lower or upper bounds. In this situation, arbitrarily small movements along a feasible search direction in the reduced problem may result in infeasibilities for basic variables in the original problem. For such cases, the search direction is typically discarded, a new reduced problem is formed and a new search direction is computed. Such a process may be extremely costly, particularly in large-scale optimization where degeneracy is likely and good search directions can be expensive to compute. This paper is concerned with a practical method for ensuring that directions that are computed in the reduced space are actually feasible in the original problem. It is based on a generalization of the ‘maximal basis’ result first introduced by Dembo and Klincewicz for large nonlinear network optimization problems. Research supported in part by NSF Grant ECS-8119513 and DOT Research Grant CT-06-0011.