具间断系数非线性抛物型方程初值问题解的渐近性质

关于二阶线性和非线性抛物型方程初值问题解的渐近性质不少作者做过研究,辜联昆最早研究了具间断系数二阶线性和拟线性抛物型方程初值问题解的渐近性质.李名德和秦禹春以及张立龙做了改进和推广,但是他们讨论的间断面仅限于直线或平面。本文利用中的思想讨论间断面为柱面的具间断系数非线性抛物型方程初值问     

初值间断的可压缩Navier-Stokes方程弱解的存在性

本文研究了粘性系数依赖密度的一维可压缩Navier-Stokes方程的初值间断问题.当初始密度间断任意大时,证明了一维可压缩Navier-Stokes方程固定边界问题整体弱解的存在唯一性,分段正则性,并给出了弱解的大时间行为等.     

用配置法解具有间断系数热传导方程的误差估计

本文用配置法求下列具有间断系数的热传导方程初边值问题的近似解本文从几方面改进[1]中的结论:1.把配置法用于具有间断系数的方程;2.指出超收敛在分割点依赖h的小邻域内产生,而不是只发生在孤立点上;3.指出在两相邻分割结点的中点上亦有超收敛现象,这一点在[1]中没有指出。     

Diffusive Regularization Inverse PINN Solutions to Discontinuous Problems北大核心CSCD

双曲守恒律方程间断问题的求解是该类方程数值求解问题研究的重点之一.采用PINN (physics-informed neural networks)求解双曲守恒律方程正问题时需要添加扩散项,但扩散项的系数很难确定,需要通过试算方法来得到,造成很大的计算浪费.为了捕捉间断并节约计算成本,对方程进行了扩散正则化处理,将正则化方程纳入损失函数中,使用守恒律方程的精确解或参考解作为训练集,学习出扩散系数,进而预测出不同时刻的解.该算法与PINN求解正问题方法相比,间断解的分辨率得到了提高,且避免了多次试算系数的麻烦.最后,通过一维和二维数值试验验证了算法的可行性,数值结果表明新算法捕捉间断能力更强、无伪振荡和抹平现象的产生,且所学习出的扩散系数为传统数值求解格式构造提供了依据.     

用配置法解抛物型方程的误差估计

配置法可用来求各种类型方程的数值解。与Galerkin方法相比,它可避免计算数值积分。Douglas等人讨论了用配置法求抛物型方程初边值问题数值解的误差。本文讨论用配置法求具有间断系数抛物型方程数值解的误差。在求近似解时,允许系数的间断点与分割点不重合。在中Douglas用配置法求热传导方程的数值解,近似解空间由属于C~1(I)中的分段四次多项式全体组成,得到在分割结点处的误差有     

一类热传导系数跳跃的非Fourier温度场分布的奇摄动双参数解

应用非Fourier热传导定律构建了温度场模型,即一类在有界域上带小参数的奇摄动双曲方程,由于温度急剧变化热传导系数出现跳跃的情况,得到了非线性的具有间断系数的奇摄动双参数双曲方程.通过奇摄动双参数展开方法,得到了该问题的渐近解;其次对热传导系数跳跃位置进行了定性分析,得到了确定热传导系数跳跃位置的计算公式,从而确定了解的形式渐近展开式;再通过余项估计,得到了渐近解的一致有效性,从而得到了完整温度场的分布.     

一维随机微分方程强解的某些结果

利用局部时及估计得到了连续半鞅型随机微分方程强解比较定理与存在唯一性定理,方程的系数可以退化可以间断。     

自适应间断Galerkin 有限元的多水平方法

本文讨论在自适应网格上间断Galerkin 有限元离散系统的局部多水平算法. 对于光滑系数和间断系数情形, 利用Schwarz 理论分析了算法的收敛性. 理论和数值试验均说明算法的收敛率与网格层数以及网格尺寸无关. 对强间断系数情形算法是拟最优的, 即收敛率仅与网格层数有关.     

Sobolev方程的时间间断Galerkin有限元方法

引入Sobolev方程的等价积分方程,构造Sobolev方程的新的时间间断Galerkin有限元格式.该格式不仅保持有限元解在时间剖分点处的间断特性,而且避免了传统时空有限元格式中跳跃项的出现,从而降低了格式理论分析和数值模拟的复杂性.证明了Sobolev方程的时间间断而空间连续的时空有限元解的稳定性、存在唯一性、L2...     

数学年刊第18卷B辑第2期(1997)目次和提要

数学年刊第１８卷Ｂ辑第２期（１９９７）目次和提要椭圆型方程内边界问题应隆安给了一个新的方法研究二阶椭圆方程内边界问题奇点附近解的正则性．对于一般的主部非对称的、具有间断的分片光滑系数的方程，证明了Ｈ１的解可以分解成两部分，一部分是对应的分片常数系数的...     

On the coupling of finite volume and discontinuous Galerkin method for elliptic problems

The coupling of cell-centered finite volume method with primal discontinuous Galerkin method is introduced in this paper for elliptic problems. Convergence of the method with respect to the mesh size is proved. Numerical examples confirm the theoretical rates of convergence. Advantages of the coupled scheme are shown for problems with discontinuous coefficients or anisotropic diffusion matrix.     

Approximations of optimal control problems for semilinear elliptic equations with discontinuous coefficients and states and with controls in the coefficients multiplying the highest derivatives

Mathematical formulations of nonlinear optimal control problems for semilinear elliptic equations with discontinuous coefficients and solutions and with controls in the coefficients multiplying the highest derivatives are studied. Finite difference approximations of optimization problems are constructed, and the approximation error is estimated with respect to the state and the cost functional. Weak convergence of the approximations with respect to the control is proved. The approximations are regularized in the sense of Tikhonov.     

On nonlinear perturbations of the Schrödinger equation with discontinuous coefficients

The results of [2] by W. J&;#228;ger and Y. Saito on the Schrödinger equation with discontinuous coefficients are extended to nonlinear perturbations of the equation.     

ON THE IDENTIFICATION OF COEFFICIENTS OF SEMILINEAR PARABOLIC EQUATIONS

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Degenerated nonlinear hyperbolic equation with discontinuous coefficients

The partial differential equations with discontinuous coefficients have been extended in various directions by a number of authors [2], [3], [11], [13], [14], [16]. This paper deals with a mixed problem for a degenerated nonlinear hyperbolic equation with discontinuous coefficients.     

Finite difference approximations of optimal control problems for semilinear elliptic equations with discontinuous coefficients and solutions

Mathematical formulation of nonlinear optimal control problems for semilinear elliptic equations with discontinuous coefficients and discontinuous solutions are examined. Finite difference approximations of optimization problems are constructed, and the approximation error is estimated with respect to the state and the cost functional. Weak convergence of the approximations with respect to the control is proved. The approximations are regularized using Tikhonov regularization.     

Multiscale discontinuous Petrov–Galerkin method for the multiscale elliptic problems

In this article, we present a new multiscale discontinuous Petrov–Galerkin method (MsDPGM) for multiscale elliptic problems. This method utilizes the classical oversampling multiscale basis in the framework of a Petrov–Galerkin version of the discontinuous Galerkin method, allowing us to better cope with multiscale features in the solution. MsDPGM takes advantage of the multiscale Petrov–Galerkin method (MsPGM) and the discontinuous Galerkin method (DGM). It can eliminate the resonance error completely and decrease the computational costs of assembling the stiffness matrix, thus, allowing for more efficient solution algorithms. On the basis of a new H² norm error estimate between the multiscale solution and the homogenized solution with the first‐order corrector, we give a detailed convergence analysis of the MsDPGM under the assumption of periodic oscillating coefficients. We also investigate a multiscale discontinuous Galerkin method (MsDGM) whose bilinear form is the same as that of the DGM but the approximation space is constructed from the classical oversampling multiscale basis functions. This method has not been analyzed theoretically or numerically in the literature yet. Numerical experiments are carried out on the multiscale elliptic problems with periodic and randomly generated log‐normal coefficients. Their results demonstrate the efficiency of the proposed method.     

Practical Stability in the pth Mean of Stochastic Differential Equations with Discontinuous Coefficients

In this paper,we give sufficient conditions to analyze the practical stability in the pth mean of stochastic differential equations with discontinuous coefficients.The Lyapunov-like function plays an important role in analysis.Some numerical computations are carried out to illustrate the theoretical results.     

On the solvability of initial boundary-value problems for a class of operator-differential equations of third order

We obtain sufficient conditions for the regular solvability of initial boundary-value problems for a class of operator-differential equations of third order with variable coefficients on the semiaxis. These conditions are expressed only in terms of the operator coefficients of the equations under study. We obtain estimates of the norms of intermediate derivative operators via the discontinuous principal parts of the equations and also find relations between these estimates and the conditions for regular solvability.