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Book "Separation of Variables and Exact Solutions to Nonlinear PDEs"

Authors:
  • Ishlinsky Institute for Problems in Mechanics of the Russian Academy of Sciences

Abstract

This book is devoted to describing and applying methods of generalized and functional separation of variables used to find exact solutions of nonlinear partial differential equations (PDEs). It also presents the direct method of symmetry reductions and its more general version. In addition, the authors describe the differential constraint method, which generalizes many other exact methods. The presentation involves numerous examples of utilizing the methods to find exact solutions to specific nonlinear equations of mathematical physics. The equations of heat and mass transfer, wave theory, hydrodynamics, nonlinear optics, combustion theory, chemical technology, biology, and other disciplines are studied. Particular attention is paid to nonlinear equations of a reasonably general form that depend on one or several arbitrary functions. Such equations are the most difficult to analyze. Their exact solutions are of significant practical interest, as they are suitable to assess the accuracy of various approximate analytical and numerical methods. The book contains new material previously unpublished in monographs. It is intended for a broad audience of scientists, engineers, instructors, and students specializing in mathematical physics, applied and computational mathematics, theoretical physics, mechanics, control theory, chemical engineering science, and other disciplines. Individual sections of the book and examples are suitable for lecture courses on partial differential equations, equations of mathematical physics, and methods of mathematical physics, for delivering special courses and for practical training.
A. D. Polyanin and A. I. Zhurov, Separation of Variables and Exact
Solutions to Nonlinear PDEs, CRC Press, Boca RatonLondon, 2022.
ISBN-978-0367486891
This book is devoted to describing and applying methods of generalized and
functional separation of variables used to find exact solutions of nonlinear partial
differential equations (PDEs). It also presents the direct method of symmetry
reductions and its more general version. In addition, the authors describe the
differential constraint method, which generalizes many other exact methods. The
presentation involves numerous examples of utilizing the methods to find exact
solutions to specific nonlinear equations of mathematical physics. The equations of
heat and mass transfer, wave theory, hydrodynamics, nonlinear optics, combustion
theory, chemical technology, biology, and other disciplines are studied. Particular
attention is paid to nonlinear equations of a reasonably general form that depend on
one or several arbitrary functions. Such equations are the most difficult to analyze.
Their exact solutions are of significant practical interest, as they are suitable to assess
the accuracy of various approximate analytical and numerical methods.
The book contains new material previously unpublished in monographs. It is
intended for a broad audience of scientists, engineers, instructors, and students
specializing in applied and computational mathematics, theoretical physics,
mechanics, control theory, chemical engineering science, and other disciplines.
Individual sections of the book and examples are suitable for lecture courses on
partial differential equations, equations of mathematical physics, and methods of
mathematical physics, for delivering special courses and for practical training.
PDF-file of the entire book is freely available on the author's personal page, see
https://eqworld.ipmnet.ru/Arts_Polyanin/Separation_of_Variables_and_Exact_
Solutions_to_Nonlinear_PDEs_2021.pdf
Article
We study the Monge–Amp`ere equation with three independent variables, which occurs in electron magnetohydrodynamics. A group analysis of this strongly nonlinear partial differential equation is carried out. An eleven-parameter transformation preserving the form of the equation is found. A formula is obtained that permits one to construct multiparameter families of solutions based on simpler solutions. Two-dimensional reductions leading to simpler partial differential equations with two independent variables are considered. One-dimensional reductions are described that permit one to obtain self-similar and other invariant solutions that satisfy ordinary differential equations. Exact solutions with additive, multiplicative, and generalized separation of variables are constructed, many of which admit representation in elementary functions. The obtained results and exact solutions can be used to evaluate the accuracy and analyze the adequacy of numerical methods for solving initial–boundary value problems described by strongly nonlinear partial differential equations.
Article
Full-text available
In this paper, we look at the method of separation of variables of a PDE from its symmetry transformation point of view. Specifically, we discuss the relation between the existence of additively and multiplicatively separated variables of a PDE, and the form of its symmetry operators. We show that solutions in the form of separated variables are in fact, invariant solutions, i.e. solutions invariant under some subalgebra of the symmetry operators of the equation. For the case of two independent variables, we obtain the form of Lie point symmetry operators corresponding to additively and multiplicatively separated solutions, and generalize our results for the case when separated variables are any functions of independent variables. We also discuss the role of contact symmetry transformations and differential invariants for the existence of separated solutions, and outline the role of variational symmetries, as well as conditional (non-classical) symmetry operators. We demonstrate that the symmetry approach is a valuable tool for obtaining information regarding existence of solutions with separated variables.
Article
We consider the multidimensional nonlinear diffusion equation with a power coefficient. Using some multidimensional quadratic ansatz, we seek for generalized automodel solutions and find new exact solutions in elementary and special functions in case of various exponents. We distinguish the events that the solutions are radially symmetric or spatially anisotropic and exhibit a series of examples demonstrating the novelty of the solutions.
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