常微分方程通解、特解、所有解的区别与联系

通过具体实例分析、讨论了高等数学中常微分方程的通解、特解和微分方程的所有解之间的区别与联系,并对高等数学教材中二阶线性微分方程的降阶法与二阶常系数非齐次线性微分方程特解求解过程中的作法进行了说明.     

n阶常系数非齐次线性微分方程的降阶解法

给出一阶线性非齐次微分方程的积分因子解法,避免了常数变易法带来的不便和不自然;给出,n阶常系数非齐次线性微分方程的降阶解法,可以看出,高阶常系数线性非齐次微分方程最终都可以归结为求解一阶线性微分方程,从而避免了待定系数法求非齐次方程特解的繁琐,并最终说明了一般微积分教材中只给出两种类型常系数非齐次线性微分方程的待定系数解法的原因．     

二阶常系数非齐次线性微分方程的通解公式

根据二阶常系数齐次线性微分方程的特征根,利用降阶法,可给出求解一般二阶常系数非齐次线性微分方程的通解公式.     

二阶变系数线性微分方程求解问题的新探索

二阶常系数线性微分方程的求解理论,目前已经比较完善.然而对于二阶变系数线性微分方程,其求解问题的研究仍处于发展状态中.本文在文献[3-5]的基础上,利用降阶法、线性变换法及Raccati方程的等价性得到若干个可写出通解的二阶变系数线性微分方程的新类型,尤其关于可转化为f″+gf=0二阶线性微分方程有了一些结果.     

二阶变系数线性微分方程的几个可积类型

利用变量代换把二阶变系数线性微分方程降阶为一阶线性微分方程,讨论了二阶变系数线性微分方程可积4个充分条件及通解公式.     

用常数变易法求微分方程特解的简单处理

简化了用"常数变易"法求常系数非齐次线性微分方程特解的过程,给出了求二阶常系数非齐次线性微分方程特解的一般公式.并将该方法推广到对n阶方程的降阶,从而求其特解.此方法简单实用,且运算量小.     

求解Bernoulli方程的常数变易法

同济大学数学教研室主编的《高等数学》教材中,把Bernoulli（伯努利）方程与一阶线性微分方程放在同一节中,一阶线性微分方程的求解使用的是常数变易法,而Bernoulli方程的解法却使用了变量代换,将其化成一阶线性微分方程后,采用常数变易法来求解．这给学生一种印象,即Bernoulli方程只能通过变量代换化成一阶线性微分方程后才能求解．作者在教学中发现,Bernoulli方程实际上可以不用通过变量代换,而直接通过常数变易方法来求解．对Bernoulli方程,与求解一阶线性微分方程一样,常数变易方法也是通过两步来完成．首先求解方程对应的…     

三阶常系数线性非齐次微分方程通解的降阶法

将降阶法应用于三阶常系数线性非齐次微分方程,对一般类型的非齐次项形式,给出了上述方程的通解公式,此外还给出了相应的应用例题.     

二阶线性微分方程组解法研究

采用降阶法和欧拉方法对一类二阶线性微分方程组的求解进行了研究,并给出了当系数矩阵的特征根为三种不同情况（互异、共轭、二重根）时微分方程组的通解公式,并通过算例验证了通解的正确性.     

用“升阶法”求解一类一阶线性微分方程——兼谈逆向思维能力的培养

"升阶法"能够把一类特殊的一阶线性微分方程化为二阶常系数齐次线性微分方程求解,而一般的一阶线性微分方程的求解问题可以转化为二元函数全微分的求积问题.利用"升阶法"和"全微分法"对学生进行逆向思维训练,培养学生的创新思维能力.     

Related solution operators in mathematical physics

Transmutation operators are derived relating many of the frequently encountered linear partial differential equations in mathematical physics. The setting for this study is vector-valued distributions. Examples are given showing how fundamental solutions are derived for both homogeneous and nonhomogeneous partial differential equations.     

任意流场中颗粒运动方程的通解(英)

给出了任意流场中颗粒运动方程的无因次和线性微分方程形式．估计了颗粒运动方程中的一些相关项．借助于一些数学推导和处理，求得了比线性颗粒运动方程的通解．     

Applications of He’s principles to partial differential equations

This paper applies the variational iteration method (VIM) and semi-inverse variational principle to obtain solutions of linear and nonlinear partial differential equations. The nonlinear model is considered from gas dynamics, fluid dynamics and Burgers equation. The linear model is the heat transfer (diffusion) equation. Results show that variational iteration method is a powerful mathematical tool for solving linear and nonlinear partial differential equations, and therefore, can be widely applied to engineering problems.     

Dynamics and exact solutions of non-evolutionary partial differential equations

The article presents a new method for constructing exact solutions of non-evolutionary partial differential equations with two independent variables. The method is applied to the linear classical equations of mathematical physics: the Helmholtz equation and the variable type equation. The constructed method goes back to the theory of finite-dimensional dynamics proposed for evolutionary differential equations by B. Kruglikov, O. Lychagina and V. Lychagin. This theory is a natural development of the theory of dynamical systems. Dynamics make it possible to find families that depends on a finite number of parameters among all solutions of PDEs. The proposed method is used to construct exact particular solutions of linear differential equations (Helmholtz equations and equations of variable type).     

A finite difference technique for solving optimization problems governed by linear functional differential equations

Aspects of the approximation and optimal control of systems governed by linear retarded nonautonomous functional differential equations (FDE) are considered. First, certain FDE are shown to be equivalent to corresponding abstract ordinary differential equations (ODE). Next, it is demonstrated that these abstract ODE may be approximated by difference equations in finite dimensional spaces. The optimal control problem for systems governed by FDE is then reduced to a sequence of mathematical programming problems. Finally, numerical results for two examples are presented and discussed.     

On reduction of some classes of partial differential equations to equations with fewer variables and exact solutions

We establish a connection between the fundamental solutions to some classes of linear nonstationary partial differential equations and the fundamental solutions to other nonstationary equations with fewer variables. In particular, reduction enables us to obtain exact formulas for the fundamental solutions of some spatial nonstationary equations of mathematical physics (for example, the Kadomtsev-Petviashvili equation, the Kelvin-Voigt equation, etc.) from the available fundamental solutions to one-dimensional stationary equations.     

Fourier–Bessel theory on flow acoustics in inviscid shear pipeline fluid flow

Flow acoustics in pipeline is of considerable interest in both industrial application and scientific research. While well-known analytical solutions exist for stationary and uniform mean flow, only numerical solutions exist for shear mean flow. Based on potential theory, a general mathematical formulation of flow acoustics in inviscid fluid with shear mean flow is deduced, resulting in a set of two second-order differential equations. According to Fourier–Bessel theory which is orthogonal and complete in Lebesgue Space, a solution is proposed to transform the differential equations to linear homogeneous algebraic equations. Consequently, the axial wave number is numerically calculated due to the existence condition of non-trivial solution to homogeneous linear algebraic equations, leading to the vanishment of the corresponding determinant. Based on the proposed method, wave propagation in laminar and turbulent flow is numerically analyzed.     

Degenerate first-order inverse problems in Banach spaces

We are concerned with an inverse problem for a degenerate linear evolution equation of first-order. Both hyperbolic and parabolic cases will be considered. We indicate sufficient conditions for the existence and uniqueness of a solution. All the results can be applied to inverse problems for equations from mathematical physics. As a possible application of the abstract theorems, some examples of partial differential equations are given.