A deep learning method for solving third-order nonlinear evolution equations

It has still been difficult to solve nonlinear evolution equations analytically. In this paper, we present a deep learning method for recovering the intrinsic nonlinear dynamics from spatiotemporal data directly. Specifically, the model uses a deep neural network constrained with given governing equations to try to learn all optimal parameters. In particular, numerical experiments on several third-order nonlinear evolution equations, including the Korteweg–de Vries (KdV) equation, modified KdV equation, KdV–Burgers equation and Sharma–Tasso–Olver equation, demonstrate that the presented method is able to uncover the solitons and their interaction behaviors fairly well.     

A deep learning method for solving high-order nonlinear soliton equations

We propose an effective scheme of the deep learning method for high-order nonlinear soliton equations and explore the influence of activation functions on the calculation results for higher-order nonlinear soliton equations. The physics-informed neural networks approximate the solution of the equation under the conditions of differential operator, initial condition and boundary condition. We apply this method to high-order nonlinear soliton equations, and verify its efficiency by solving the fourth-order Boussinesq equation and the fifth-order Korteweg–de Vries equation. The results show that the deep learning method can be used to solve high-order nonlinear soliton equations and reveal the interaction between solitons.     

非线性离散微分方程的双曲函数法求解

本文推广了双曲函数方法用于求解非线性离散系统。求解离散的(2+1)维Toda系统和离散的mKdV系统，成功地得到了离散钟型孤立子、离散冲击波型孤立子及一些新的精确行波解。     

The modified simple equation method for solving some fractional-order nonlinear equations

Nonlinear fractional differential equations are encountered in various fields of mathematics, physics, chemistry, biology, engineering and in numerous other applications. Exact solutions of these equations play a crucial role in the proper understanding of the qualitative features of many phenomena and processes in various areas of natural science. Thus, many effective and powerful methods have been established and improved. In this study, we establish exact solutions of the time fractional biological population model equation and nonlinear fractional Klein–Gordon equation by using the modified simple equation method.     

On a certain method of solving nonlinear differential equations

A new method of exactly solving nonlinear differential partial equations is developed. This method is applied to an equation of a potential flow of compressible gas. A new solution is obtained in the supersonic region, which may be treated as an analogon of a nonlinear stationary wave.Partially supported by NSF contract INT 73-20002A01.     

A new method for solving perturbation equations

A new, generally applicable technique is described for constructing solutions of a coupled linear system of partial differential equations when a decoupled equation has been derived. This method has already yielded an extremely simple derivation of perturbation formulas given by Cohen and Kegeles and by Chrzanowski as well as new formulas for the complete solutions of the coupled Einstein-Maxwell equations describing Reissner-Nordström perturbations. It is hoped that it will prove valuable for many other applications.This essay received the third award from the Gravity Research Foundation for the year 1979-Ed.     

Whittaker方程的场方法

用场方法来求解Whittaker方程.将一个场变量取作为其余场变量和时间的函数并对这个函数建立基本偏微方程.如能求得它的完全积分，那么Whittaker方程的解可由解代数方程来得到. 关键词： 场变量 基本偏微分方程 场方法 积分     

A method for solving phase transition equations

The kinetics of phase transitions is calculated on the assumption of mechanical and temperature equilibrium between mixture components. The simulation of kinetics is based on solving relaxation-type kinetic equations. The deviator components of the constituents of a mixture of phases are assumed to be equal. When a material is deformed, several phase transitions can occur simultaneously. The determination of the thermodynamic parameters of mixture components is based on solving linearized equations for component pressure and temperature increments at known specific volume and mixture energy increments. We suggest an effective algorithm for solving these equations. The algorithm is based on an explicit Lagrangian difference scheme and takes into account pressure and temperature discrepancies. The algorithm is implemented in the SPRUT two-dimensional program. We present the results of calculations for one-and two-dimensional problems with and without taking into account the α-? transition in iron.     

Transformation methods for solving nonlinear field equations

The collection of extended canonical transformations of first-order contact manifolds is studied. This collection is shown to form a group under target-source composition and to contain the group of all first prolongations of point transformation of the underlying graph space and all isogroups of completely integrable horizontal ideals. Extended canonical transformations are compared and contrasted with Bäcklund transformations. These results are used to construct an extended Hamilton-Jacobi method for systems of nonlinear PDE. The collection of all extended canonical transformations is also shown to contain infinitely many one-parameter families of transformations, but there is no Lie group structure that contains these one-parameter families, in general. Conditions are obtained under which a one-parameter family of extended canonical transformations will map a solution of the fundamental ideal that characterizes a given system of PDE into a one-parameter family of solutions. These results are applied to the -Gordon equation _x1 = () and to the Navier-Stokes equations.     

一类强非线性发展方程孤波变分迭代解法

研究了一类强非线性发展方程. 利用变分迭代方法,首先构造了相应的变分;其次选取了适当的初始近似;再用迭代方法得到了孤波的任意次精度的近似解. 关键词： 发展方程 非线性 孤波 近似方法.     

非线性波方程尖峰孤子解的一种简便求法及其应用

根据尖峰孤子解的特点,提出了一种待定系数法求非线性波方程尖峰孤子解的思路和方法,并利用该方法求解了5个非线性波方程,即CH（Camassa-Holm)方程、五阶KdV-like 方程、广义Ostrovsky方程、组合KdV-mKdV方程和Klein-Gordon方程,比较简便地得到了这些方程的尖峰孤子解.文献中关于CH方程的结果成为本文结果的特例.通过数值模拟给出了部分解的图像.简要说明了非线性波方程存在尖峰孤子解所须满足的特定条件.该方法也适用于求其他非线性波方程的尖峰孤子解. 关键词： 非线性波方程 尖峰孤子解 待定系数法     

A different method for solving the Hartree-Fock equations

A method is presented which guarantees the convergence of the solution of HF equations.     

Improved algorithm for solving nonlinear parabolized stability equations

Due to its high computational efficiency and ability to consider nonparallel and nonlinear effects, nonlinear parabolized stability equations(NPSE) approach has been widely used to study the stability and transition mechanisms. However,it often diverges in hypersonic boundary layers when the amplitude of disturbance reaches a certain level. In this study, an improved algorithm for solving NPSE is developed. In this algorithm, the mean flow distortion is included into the linear operator instead of into the nonlinear forcing terms in NPSE. An under-relaxation factor for computing the nonlinear terms is introduced during the iteration process to guarantee the robustness of the algorithm. Two case studies, the nonlinear development of stationary crossflow vortices and the fundamental resonance of the second mode disturbance in hypersonic boundary layers, are presented to validate the proposed algorithm for NPSE. Results from direct numerical simulation(DNS) are regarded as the baseline for comparison. Good agreement can be found between the proposed algorithm and DNS, which indicates the great potential of the proposed method on studying the crossflow and streamwise instability in hypersonic boundary layers.     

On spectral methods for solving nonlinear acoustics equations

Two very efficient methods for obtaining approximate solutions to nonlinear acoustics equations are discussed. I proposed these methods earlier, but they are still little known. The first method is based on expanding an unknown function into a Taylor series with respect to the coordinate (evolution variable) and on approximate summation of the terms of this series in all orders up to the infinite order. This series can be summed completely only in particular cases, e.g., for a simple wave. It has been noted that the partial summation technique is implemented more easily if all the terms of the series are represented as corresponding topological diagrams. The second method is based on introducing a “nonlinear” phase delay (proportional to the wave amplitude) for the temporal variable in linear solutions of the problem. The application technique of these methods is illustrated by obtaining approximate solutions of the Burgers equation.     

同伦分析法在求解非线性演化方程中的应用

利用同伦分析法求解了(2+1)维改进的 Zakharov-Kuznetsov方程, 得到了它的近似周期解,该解与精确解符合很好. 结果表明，同伦分析法在求解高维非线性演化方程时, 仍然是一种行之有效的方法. 同时,还对该方法进行了一定的扩展， 经过扩展后的方法能够更方便地求解更多非线性演化方程的高精度近似解析解. 关键词： 同伦分析法 改进的 Zakharov-Kuznetsov方程 周期解     

求解微分方程的Hojman方法

首先，将Hojman用于求解二阶微分方程组守恒量的方法推广并应用于一阶微分方程组，特别是奇数维微分方程组的积分问题.然后，证明 Hojman定理是本文定理的特殊情形.最后，举例说明结果的应用. 关键词： 微分方程 Hojman定理 守恒量 积分     

A Birkhoff-Noether method of solving differential equations

In this paper, a Birkhoff--Noether method of solving ordinary differential equations is presented. The differential equations can be expressed in terms of Birkhoff's equations. The first integrals for differential equations can be found by using the Noether theory for Birkhoffian systems. Two examples are given to illustrate the application of the method.     

A splitting extrapolation for solving nonlinear elliptic equations with d-quadratic finite elements

Nonlinear elliptic partial differential equations are important to many large scale engineering and science problems. For this kind of equations, this article discusses a splitting extrapolation which possesses a high order of accuracy, a high degree of parallelism, less computational complexity and more flexibility than Richardson extrapolation. According to the problems, some domain decompositions are constructed and some independent mesh parameters are designed. Multi-parameter asymptotic expansions are proved for the errors of approximations. Based on the expansions, splitting extrapolation formulas are developed to compute approximations with high order of accuracy on a globally fine grid. Because these formulas only require us to solve a set of smaller discrete subproblems on different coarser grids in parallel instead of on the globally fine grid, a large scale multidimensional problem is turned into a set of smaller discrete subproblems. Additionally, this method is efficient for solving interface problems.     

Functional method for solving gravitational field equations

A new method for solving the equations of a gravitational field (G field), which is based on functional transformations (FT), which replace holonomic transformations (HT), is discussed. The method is equivalent to nonholonomic transformations (NT) of the field functions and makes it possible to use a known solution to construct a new set of solutions in the same coordination, which contains a fixed number (up to 12) of arbitrary functions. The FT method can be used to solve the Cauchy problem for a non-steady-state G field, to eliminate singularities in the field, etc.This article is published as a matter for discussion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 50–55, February, 1979.     

Variational iteration method for solving biharmonic equations

By means of the variational iteration method the numerical solution of biharmonic equations are obtained. Biharmonic equation has significant applications in physics and engineering. There is a difficulty to solve the biharmonic equation due to the existence of fourth order derivatives. For this reason, we use the variational iteration method to solve this equation. Test problems, are used to validate this algorithm which is found to be more accurate and efficient than previous ones.