一个水动力泥沙数学模型的伴随算子法敏感性分析

本文报告了把一种高效率的敏感性分析方法一伴随算子法应用到一十水动力泥沙模型的一些初步工作。本文的目的和动机一是问答能否将伴随算子方法应用到包含多种时间尺物理过程的水动力泥抄数学模型中。二是探讨将所得到的敏感性信息如何应甩到与水刹、泥泥工程有关的问题中。将伴随算子方法应用到二维水动力泥沙数学模型中是完全可行的。尽管在数学模型中存在不可微的奇点．由于它们都是孤立的．利用分段求导可以构造伴随模型。     

Optimal control problems related to the navigation channel engineering

The navigation channel engineering poses optimal control problems of how to find the optimal way of engineering such that the water depth of the channel is maximum under certain budget constraint, or the cost of me en-gineering is minimum while certain goals are achieved. These are typical control problems of distributed system gov erned by hydraulic/sedimentation models. The problems and methods of solutions are discussed Since the models, usually complicated, are nonlinear, they can be solved by solving a series of linear problems For linear problems the solutions are given. Thus the algorithms are simplified.     

Computational uncertainty principle in nonlinear ordinary differential equations——Ⅱ.Theoretical analysis

The error propagation for general numerical method in ordinary differential equations ODEs is studied. Three kinds of convergence, theoretical, numerical and actual convergences, are presented. The various components of round-off error occurring in floating-point computation are fully detailed. By introducing a new kind of recurrent inequality, the classical error bounds for linear multi-step methods are essentially improved, and joining probabilistic theory the "normal" growth of accumulated round-off error is derived. Moreover, a unified estimate for the total error of general method is given. On the basis of these results, we rationally interpret the various phenomena found in the numerical experiments in part I of this paper and derive two universal relations which are independent of types of ODEs, initial values and numerical schemes and are consistent with the numerical results. Furthermore , we give the explicitly mathematical expression of the computational uncertainty principle and expound the i     

Computational uncertainty principle in nonlinear ordinary differential equations (I)——Numerical results

In a majority of cases of long-time numerical integration for initial-value problems, roundoff error has received little attention. Using twenty-nine numerical methods, the influence of round-off error on numerical solutions is generally studied through a large number of numerical experiments. Here we find that there exists a strong dependence on machine precision (which is a new kind of dependence different from the sensitive dependence on initial conditions), maximally effective computation time (MECT) and optimal stepsize (OS) in solving nonlinear ordinary differential equations (ODEs) in finite machine precision. And an optimal searching method for evaluating MECT and OS under finite machine precision is presented. The relationships between MECT, OS, the order of numerical method and machine precision are found. Numerical results show that round-off error plays a significant role in the above phenomena. Moreover, we find two universal relations which are independent of the types of ODEs, initial val     

关于自然科学学术期刊纳入公益性事业管理的建议

党的十六大以来，文化事业体制改革进一步深化。2005年，新闻出版改革在试点工作的基础上拟全面推开。中央把文化单位分为两大类：一类是公益性的事业，即为公共事业服务、隶属于国家的一些事业性质的部门；另一类是经营性的产业，它以生产的产品上市，通过市场实现它的价值。同时，中央对区分新闻出版单位的性质的问题提出了明确的界定，     

一个近岸海流数值计算模式及其检验

本文介绍一个简单的近岸海流数值计算模式。该模式以二维全流方程为基础,采用等距、跳点、隐式的总能量守恒型有限差分方案,在计算中差分方程组被分裂为适应过程、发展过程和耗散过程等三个方程组依次求解,通过若干实例的具体计算,对该模式的计算稳定性和数值模拟能力进行了检验,所得结果令人鼓午。