2007年高考中解析几何存在性问题浅析

涉及到某种数学对象是否存在的问题，常称为存在性问题，存在性问题根据其问题特征大体可以分为如下三类：1）证明某种对象一定存在，可以称为“肯定型问题”；2）证明某种对象一定不存在，可以称为“否定型问题”；3）探究某种对象是否存在，或者探究某类对象存在的条件，可以称为“探究型存在性问题”。     

带双参数的半线性椭圆方程正解存在与不存在性以及一个预值结论

研究带有双参数的半线性椭圆方程在Robin边界下正解的存在与不存在性.证明了对任意的边界参数c(0c∞),存在λ*=λ*(c)∞,当0λ≤λ*,方程存在一个最小解u_λ,而任意其它的解是对应抛物方程整体解存在与不存在的一个预值.     

二阶Sturm-Liouville特征值问题解的存在与非存在性

讨论了二阶Sturm-Liouville特征值边值问题解的存在性与非存在性,得到了边值问题至少有一个正解的特征值λ的存在区间的结论.进一步,给出了边值问题没有正解的特征值存在区间.     

一类具交错扩散的强耦合退化抛物方程组解的整体存在与非存在性

本文研究了一类具交错扩散的强耦合拟线性退化抛物方程组初边值问题正古典解的局部存在,整体存在与非整体存在性.利用正则化方法和先验估计技巧证明了该问题正古典解的局部存在性,并且分别给出了该问题是否存在整体古典解的充分条件.结果表明当种群内竞争强于种群间互惠作用时,此问题存在整体解;而当两种群具有强互惠作用时,所有解都是非整体的.     

一类平面五次系统的极限环

研究了一类生化反应模型得到了极限环不存在或存在唯一的如下条件：１）若Ｐ＜０，则系统（１）存在唯一稳定的极限环．２）若Ｐ≥０．则系统（１）不存在极限环．     

非线性算子的歧点

本文研究了Banach空间中非线性全连续算子在不假设Fréchet可微的条件下,歧点的存在性和不存在性.利用齐次算子,获得了这类算子歧点的存在和不存在的充分条件,推广和改进了已有文献中的结果.     

非线性系统有理首次积分的不存在性和部分存在性

该文的目的是给出一般非线性系统存在和部分存在有理首次积分的判别准则. 作者给出系统存在有理首次积分的必要条件, 在此基础上进一步给出系统不存在其它有理首次积分(在函数独立的意义下)的判定准则.     

具有Strum—Liouville边界条件的四阶奇异超线性微分方程正解的存在性和不存在性

本文给出Strum-Liouville边界条件下的一类四阶奇异超线性微分方程其C2[0,1]正解存在的充分必要条件和C3[0,1]正解存在的充分条件和必要条件.结果可用于判断给定的边值问题其正解的存在性与不存在性.     

具时滞的神经网络模型的非平凡周期解的全局存在性

本文考虑具时滞的n维神经网络模型.利用FDE的全局Hopf分支存在定理和Bendixson周期解不存在定理,给出该模型存在非平凡周期解的条件.     

广义Davey-Stewartson方程组的整体解及自相似解

本文研究Dalvey-Stewartson方程组的整体解与自相似解的存在性.首先,运用Ba- nach不动点定理得到一个关于解整体存在性的一般性定理,然后把一类特殊的初始值用到该存在性结果上去从而得到自相似解存在的结论.     

A nonlinear singular eigenvalue problem for a linear system of ordinary differential equations with redundant conditions

A nonlinear eigenvalue problem for a linear system of ordinary differential equations is examined on a semi-infinite interval. The problem is supplemented by nonlocal conditions specified by a Stieltjes integral. At infinity, the solution must be bounded. In addition to these basic conditions, the solution must satisfy certain redundant conditions, which are also nonlocal. A numerically stable method for solving such a singular overdetermined eigenvalue problem is proposed and analyzed. The essence of the method is that this overdetermined problem is replaced by an auxiliary problem consistent with all the above conditions.     

Step-like contrast structure for a quasilinear system of singularly perturbed differential equations with a zero characteristic number

We consider a system of singularly perturbed first-order differential equations with a zero characteristic number. The solution of such a problem is characterized by the presence of a contrast structure, that is, of an internal transition layer on a given interval. We prove the existence of an exact solution with a step-like contrast structure and construct its uniform asymptotic expansion. An example is given.     

Discretized Energy Minimization in a Wave Guuide with point Sources

An anti-noise problem on a finite time interval is solved by minimization of a quadratic functional on the Hilbert space of square integrable controls. To this end, the one-dimensional wave equation with point sources and pointwise reflecting boundary conditions is decomposed into a system for the two propagating components of waves. Wellposedness of this system is proved for a class of data that includes piecewise linear initial conditions and piecewise constant forcing functions. It is shown that for such data the optimal piecewise constant control is the solution of a sparse linear system. Methods for its computational treatment are presented as well as examples of their applicability. The convergence of discrete approximations to the general optimization problem is demonstrated by finite element methods.     

Formal solution of an interval system of linear equations with an application in static responses of structures with interval forces

We are concerned with the so called formal solution of an interval system of linear equations. We focus on the case where the coefficient matrix is deterministic (real) and the right-hand side is an interval vector. We show that the set of formal solutions represents a convex polyhedral set. We propose new properties of the formal solution related to its existence, uniqueness and robustness. As particular classes of problems we investigate also the situation where the coefficient matrix is an M-matrix or H-matrix. Example problems related to the structures, such as 6-bar truss and a rectangular sheet, are solved to illustrate the computational aspects of the methods.     

Solving Linear Systems Whose Elements Are Nonlinear Functions of Intervals

The paper addresses the problem of solving linear algebraic systems the elements of which are, in the general case, nonlinear functions of a given set of independent parameters taking on their values within prescribed intervals. Three kinds of solutions are considered: (i) outer solution, (ii) interval hull solution, and (iii) inner solution. A simple direct method for computing a tight outer solution to such systems is suggested. It reduces, essentially, to inverting a real matrix and solving a system of real linear equations whose size n is the size of the original system. The interval hull solution (which is a NP-hard problem) can be easily determined if certain monotonicity conditions are fulfilled. The resulting method involves solving n+1 interval outer solution problems as well as 2n real linear systems of size n. A simple iterative method for computing an inner solution is also given. A numerical example illustrating the applicability of the methods suggested is solved.     

Adaptive Interpolation Algorithm Based on a kd-Tree for Numerical Integration of Systems of Ordinary Differential Equations with Interval Initial Conditions

We consider issues related to the numerical solution of interval systems of ordinary differential equations. We suggest an algorithm that permits finding interval estimates of solutions with prescribed accuracy in reasonable time. The algorithm constructs an adaptive partition (a dynamic structured grid) based on a kd-tree over the space formed by interval initial conditions for the ordinary differential equations. In the operation of the algorithm, a piecewise polynomial function interpolating the dependence of the solution on the specific values of interval parameters is constructed at each step of solution of the original problem. We prove that the global error estimate linearly depends on the height of the kd-tree. The algorithm is tested on several examples; the test results show its efficiency when solving problems of the class under study.     

非线性分数阶微分方程解的延拓

本文研究了分数阶微分方程(1.1)解的延拓问题.利用解的表达式给出方程解的可延拓条件,在此基础上研究了解可以延拓至何种程度的有关结果,且探讨了解的存在区间为[to,+∞)的条件.     

On Linear Inequality Systems with Smooth Coefficients

A linear inequality system with infinitely many constraints is polynomial [analytical] if its index set is a compact interval of the real line and all its coefficients are polynomial [analytical] functions of the index on this interval. This paper provides sufficient conditions for a given closed convex set to be the solution set of a certain polynomial or at least analytical system.The authors are indebted to Dr. J. M. Almira for valuable comments and suggestions.     

On approximate methods of analysing certain singularly-perturbed systems

A certainclass of sigularly-perturbed systems which have a variety of m-dimensional stationary positions is considered. When a small parameter disappears, the system also has an m-dimensional manifold of stationary positions and, therefore, the corresponding characteristic equation has m zero roots. The conditions under which the solution of a stability problem reduces to the same problem for a degenerate system are defined. As an application in practice gyroscopic stabilizing systems (the critical case corresponds to such systems) with elastic elements of high stiffness are discussed. The conditions under which the solution of the problem of the stability of steady motion follows from the solution of this problem for an ideal system (with absolutely rigid elements) are obtained. The problem of the closeness of the corresponding solutions of the complete and a simplified system of differential equations over an infinite time interval is discussed.     

多体系统动力学微分-代数方程L-稳定方法

针对多体系统动力学微分-代数方程形式，在时间区间上构造L-稳定方法，分别基于等距节点、Chebyshev节点和Legendre节点等非等距节点建立求解格式，依据Ehle定理及猜想，与Padé逼近式对比得到待定矩阵和向量，从而获得L-稳定求解公式，循环求解过程采用Newton迭代法计算.以平面双连杆机械臂系统为例，使用L-稳定方法进行数值仿真，通过改变时间区间节点数和步长对各个指标结果进行比较，并与经典Runge-Kutta法对比.结果表明，该方法具有稳定性好、精度高等优点，适用于长时间情况下的多体系统动力学仿真.