The importance of the nonlinear systems due to their common occurrence in the study of physical phenomena and also the various limitations posed by the linear systems theory have been the prime reasons for the studies of nonlinear models as such. The physical situations in which nonlinear equations arise tend to be highly idealized with the assumption of constant coefficients. Due to this, much attention has been paid on study of nonlinear equations with variable coefficients. This book deals with nonlinear partial differential equations with variable coefficients representing some interesting physical systems viz. coupled KdV system, generalized Hirota-Satsuma KdV, variant Boussinesq, modified Boussinesq and a family of non-evolution equations, from the view point of their underlying Lie point symmetries and to obtain their exact solutions. Since the nonlinear systems with variable coefficients are very difficult to handle, hence this book shall provide freedom for the researchers to obtain the symmetries and exact solutions for variable coefficients nonlinear systems and further to simulate the desired physical situations.

This book deals with applications of symmetry groups to solve physically important Einstein field equations, which are-the nondiagonal Einstein-Rosen metrics, the Einstein-Maxwell equations, Einstein-Maxwell equations for the magnetostatic fields, the Einstein-Maxwell equations for non-static Einstein and Rosen metrics, Einstein Vacuum equations for axially symmetric gravitational fields. To solve these highly nonlinear systems of partial differential equations (PDEs), Lie Classical method, symmetry reduction method and (G'/G)-expansion method are utilized. Symmetries are derived to reduce these systems of PDEs to ODEs and some exact solutions are obtained. Some of these solutions are also represented graphically.

Keeping in view the rich treasure and wide applicability of nonlinear equations in almost every field, we have in this book carried out the application of Lie group analysis for obtaining exact solutions to nonlinear partial differential equations. In particular, this book is devoted to a wide range of applications of continuous symmetry groups to two physically important systems i.e. the (2+1)-dimensional Calogero Degasperis equation with its variable coefficients form and the (2+1)-dimensional potential Kadomstev Petviashvili equation along its generalized form. In recent years, much attention has also been paid to equations with variable coefficients as the physical situations in which nonlinear systems arise tend to be highly idealized due to assumption of constant coefficients. This has led us to undertake the study of equations with variable coefficients and to derive the admissible forms of the coefficients along with their exact solutions. The efforts are thus concentrated on finding the symmetries, reductions and exact solutions of certain nonlinear equations by using various methods.

This book deals with wide range of applications of continuous symmetry groups to some physically important systems which are: the coupled Klein-Gordon-Schrodinger equation with its generalized form, the Dullin-Gottwald-Holm Equation, the Generalized Bretherton equation with variable coefficients. For all the three different equations, we have derived some special type of solutions including traveling wave solutions, periodic solutions, kink wave solutions, solitons etc. and we have plotted some figures also to see the propogation and asymptotic behaviour of all types of waves.

This book is an outgrowth of our results on the existence and stability of solutions to nonlinear dynamical systems, stochastic systems, and impulsive systems over the last five years. In particular, we present the Razumikhin-type exponential stability criteria for impulsive stochastic functional differential systems, the stability analysis of neutral stochastic delay differential equations by a generalization of Banachs contraction principle and the globally asymptotical stability in the mean square for stochastic neural networks with time-varying delays and fixed moments of impulsive effect. Also, we discuss oscillation criteria based on a new weighted function for linear matrix Hamiltonian systems and the existences of the positive solutions or nontrivial solutions of nonlinear differential equations.

General relativity is a physical theory which nowadays plays a key role in astrophysics and in physics and in this way it is important for a number of ambitious experiments and space missions. Einstein equations are central piece of general relativity. Einstein equations are expressed in terms of coupled system of highly nonlinear partial differential equations describing the matter content of space-time. The present work is to give an exposition of parts of the theory of partial differential equations that are needed in this subject and to represent exact solutions to Einstein equations. This book deals with various system of non linear partial differential equations corresponding to the Einstein equations for non diagonal Einstein-Rosen Metrics, Cylindrically Symmetric Null Fields, Vacuum Field Equations etc. from the view point of underlying symmetries and then to obtain their some new explicit exact solutions by using symmetry techniques like Lie symmetry analysis, symmetry reduction etc. These exact solutions play a significant for understanding of various phenomenons and are utilized for checking validity of numerical and approximation techniques and programs.

Exact solutions to nonlinear evolution equations (NEEs) play an important role in nonlinear physical science, since the characteristics of these solutions may well simulate real-life physical phenomena. One of the benefits of finding new exact solutions to such nonlinear partial differential equations (PDEs) is to give a better understanding on the various characteristics of the solutions. The main task of this work is to show that our proposed methods, improved tanh and sech methods, are very efficient in solving various types of NEEs and PDEs including special equations than using classical tanh and sech methods. This efficiency is because of their rich with the multiple traveling wave solutions than classical tanh and sech methods. From the obtained results, we can not only recover the previous solutions obtained by some authors but also obtain some new and more general solitary wave, singular solitary wave and periodic solutions. Illustrating the theory of nonlinear transmission lines (NLTLs), showing the ability of NLTL to generate solitons and solving the model equation of NLTL in presence of loss are other tasks of this book.

Nonlinear problems are of interest to engineers, physicists and mathematicians and many other scientists because most systems are inherently nonlinear in nature. As nonlinear equations are difficult to solve, nonlinear systems are commonly approximated by linear equations. This works well up to some accuracy and some range for the input values, but some interesting phenomena such as chaos and singularities are hidden by linearization and perturbation analysis. It follows that some aspects of the behavior of a nonlinear system appear commonly to be chaotic, unpredictable or counterintuitive. Although such a chaotic behavior may resemble a random behavior, it is absolutely deterministic. Analytical Routes to Chaos in Nonlinear Engineering discusses analytical solutions of periodic motions to chaos or quasi-periodic motions in nonlinear dynamical systems in engineering and considers engineering applications, design, and control. It systematically discusses complex nonlinear phenomena in engineering nonlinear systems, including the periodically forced Duffing oscillator, nonlinear self-excited systems, nonlinear parametric systems and nonlinear rotor systems. Nonlinear models used in engineering are also presented and a brief history of the topic is provided. Key features: Considers engineering applications, design and control Presents analytical techniques to show how to find the periodic motions to chaos in nonlinear dynamical systems Systematically discusses complex nonlinear phenomena in engineering nonlinear systems Presents extensively used nonlinear models in engineering Analytical Routes to Chaos in Nonlinear Engineering is a practical reference for researchers and practitioners across engineering, mathematics and physics disciplines, and is also a useful source of information for graduate and senior undergraduate students in these areas.

The study of nonlinear oscillators equations is of great importance not only in all areas of physics but also in engineering and other disciplines, since most phenomena in our word are nonlinear and are described by nonlinear equations. Recently, considerable attention has been direct towards the analytical solutions for nonlinear oscillators, for example, elliptic homotopy averaging method, amplitude-frequency formulation, homotopy perturbation method, parameter-expanding method, energy balance method, and others. The aim of this thesis is to study the periodic solutions for some physical systems which the mathematical formulation of these systems leads to a certain set of nonlinear ordinary differential equations of the second order.

The Boundary value/periodic problems for the nonlinear equation (or, more generally, second order nonlinear ODEs) have been the focus of nonlinear analysis study for a long time. The goal of this book is to show how the equivariant degree theory can be used for the systematic study of multiple solutions to several (symmetric) generalizations of BVP and for the classification of symmetric properties of these solutions. There are several classical methods of nonlinear analysis used to solve the BVP. However, their application encounters serious difficulties if: the group of symmetries is large, the dimension of the problem is high, and multiplicities of eigenvalues of linearizations are large, etc. In this book, we: (i) set up the abstract functional analysis framework for studying symmetric properties of multiple solutions to symmetric generalizations of the BV problem via the equivariant degree approach; (ii) describe wide classes of second order BVPs admitting dihedral symmetries to which the abstract theory can be effectively applied; (iii) and apply the obtained results to several classes of implicit second order symmetric differential equations.

In this book, we study the validity of the maximum principle (one of the most useful and best known tools employed in the study of partial differential equations) for some nonlinear elliptic systems, with variable coefficients, involving the weighted p-Laplcaian operators on bounded and unbounded domains. Also, using a different methods like the nonlinear theory of monotone operators, subsuper solutions method and an approximation (perturbation) method, we study the existence of positive weak solutions for some nonlinear elliptic systems, with variable coefficients, involving the weighted p-Laplcaian operators on bounded and unbounded domains.

The reader is about to embark on a tutorial journey through a series of nonlinear dynamic systems that contain a rich tapestry of phenomena and solutions. The study of nonlinear systems can be greatly enhanced by the combined use of the stochastic dynamic equations and Monte Carlo calculations. When a dynamic system is forced and dissipative all the trajectories tend toward a bounded set of zero volume - often a strange attractor with a fractal dimension. The stochastic dynamic equations can directly reveal the statistical moments of the system, but their direct solution is inefficient, and they are not a closed set. The power of the combined method is that the time averaged Monte Carlo moments will agree exactly with equations described by the left hand side of the full stochastic dynamic equations set to zero - no closure is required. Every equation expresses an exact relationship among the variables. One is able to delve far deeper into the nature of the nonlinear systems. This tutorial exposition offers the tools for the past nonlinear modeling efforts in the traditional physical sciences and in various complex modeling problems in new fields of biology and health sciences.

This book focuses on exact construction of moving excitations in nonlinear dissipative lattice systems. The lattice structure arises from the interaction among units discretely distributed in space where each unit follows a nonlinear evolution dynamics. The class of systems we consider includes Nagumo and FitzHugh-Nagumo (FHN) type pde’s. In each of these we replace the commonly considered cubic nonlinearity with an appropriate piecewise linear one. This reduces the problem of exact construction of the moving excitations to one of constructing the general solution of a linear evolution equation in terms of the eigenmodes in appropriate intervals of the relevant propagation variable and a matching of the solutions across those intervals. As solutions of discrete Nagumo model we construct two classes of fronts: kink and antikink, which are related through a symmetry transformation. The solutions to discrete FHN systems are the pulse and pulse-trains constructed on the basis of singular perturbation technique where a conjugate pair of kink and antikink form the leading and trailing edges of the pulse, the two being joined up through the slow evolution of a recovery variable.

It is well known that nonlinear evolution equations (NLEEs) are widely used to describe physical phenomena in various scientific and engineering fields, such as fluid mechanics, plasma physics, optical fibers, biology, solid state physics, etc. In order to understand the mechanisms of those physical phenomena, it is necessary to explore their solutions and properties. Solutions for the NLEEs can not only describe the designated problems, but also give more insights on the physical aspects of the problems in the related fields. In recent years, various powerful methods have been presented for finding exact solutions of the NLEEs in mathematical physics. The main purpose of this book is to illustrate how to establish solitary and periodic solutions of many NLEEs. Many illustrative examples are discussed by different methods, enjoy reading it.

Differential equations are encountered in various fields such as physics, chemistry, biology, mathematics and engineering. Most nonlinear models of real-life problems are still very difficult to solve either numerically or theoretically. Many unrealistic assumptions have to be made to make nonlinear models solvable. There has recently been much attention devoted to the search for better and more efficient solution methods for determining a solution, approximate or exact, analytical or numerical, to nonlinear models. Finding exact/approximate solutions of these nonlinear equations are interesting and important. One of these methods is variational iteration method (VIM), which has been proposed by Ji-Huan He in 1997 based on the general Lagrange’s multiplier method. The main feature of the method is that the solution of the linearized problem is used as the initial approximation for the linear and nonlinear problems. Then a more highly precise approximation at some special point can be obtained. This approximation converges rapidly to an accurate solution. VIM is very powerful and efficient in finding analytical as well as numerical solutions for a wide class of differential equation

## symmetries and exact solutions for nonlinear systems в наличии / купить интернет-магазине

## Symmetries and Exact Solutions for Nonlinear Systems

The importance of the nonlinear systems due to their common occurrence in the study of physical phenomena and also the various limitations posed by the linear systems theory have been the prime reasons for the studies of nonlinear models as such. The physical situations in which nonlinear equations arise tend to be highly idealized with the assumption of constant coefficients. Due to this, much attention has been paid on study of nonlinear equations with variable coefficients. This book deals with nonlinear partial differential equations with variable coefficients representing some interesting physical systems viz. coupled KdV system, generalized Hirota-Satsuma KdV, variant Boussinesq, modified Boussinesq and a family of non-evolution equations, from the view point of their underlying Lie point symmetries and to obtain their exact solutions. Since the nonlinear systems with variable coefficients are very difficult to handle, hence this book shall provide freedom for the researchers to obtain the symmetries and exact solutions for variable coefficients nonlinear systems and further to simulate the desired physical situations.

## Symmetries and Exact Solutions OF Einstein Field Equations

This book deals with applications of symmetry groups to solve physically important Einstein field equations, which are-the nondiagonal Einstein-Rosen metrics, the Einstein-Maxwell equations, Einstein-Maxwell equations for the magnetostatic fields, the Einstein-Maxwell equations for non-static Einstein and Rosen metrics, Einstein Vacuum equations for axially symmetric gravitational fields. To solve these highly nonlinear systems of partial differential equations (PDEs), Lie Classical method, symmetry reduction method and (G'/G)-expansion method are utilized. Symmetries are derived to reduce these systems of PDEs to ODEs and some exact solutions are obtained. Some of these solutions are also represented graphically.

## Applications of Lie Group to Some Nonlinear Equations

Keeping in view the rich treasure and wide applicability of nonlinear equations in almost every field, we have in this book carried out the application of Lie group analysis for obtaining exact solutions to nonlinear partial differential equations. In particular, this book is devoted to a wide range of applications of continuous symmetry groups to two physically important systems i.e. the (2+1)-dimensional Calogero Degasperis equation with its variable coefficients form and the (2+1)-dimensional potential Kadomstev Petviashvili equation along its generalized form. In recent years, much attention has also been paid to equations with variable coefficients as the physical situations in which nonlinear systems arise tend to be highly idealized due to assumption of constant coefficients. This has led us to undertake the study of equations with variable coefficients and to derive the admissible forms of the coefficients along with their exact solutions. The efforts are thus concentrated on finding the symmetries, reductions and exact solutions of certain nonlinear equations by using various methods.

## Symmetries and Invariant Solutions to Some Nonlinear Systems

This book deals with wide range of applications of continuous symmetry groups to some physically important systems which are: the coupled Klein-Gordon-Schrodinger equation with its generalized form, the Dullin-Gottwald-Holm Equation, the Generalized Bretherton equation with variable coefficients. For all the three different equations, we have derived some special type of solutions including traveling wave solutions, periodic solutions, kink wave solutions, solitons etc. and we have plotted some figures also to see the propogation and asymptotic behaviour of all types of waves.

## Existence and stability of solutions to nonlinear dynamical systems

This book is an outgrowth of our results on the existence and stability of solutions to nonlinear dynamical systems, stochastic systems, and impulsive systems over the last five years. In particular, we present the Razumikhin-type exponential stability criteria for impulsive stochastic functional differential systems, the stability analysis of neutral stochastic delay differential equations by a generalization of Banachs contraction principle and the globally asymptotical stability in the mean square for stochastic neural networks with time-varying delays and fixed moments of impulsive effect. Also, we discuss oscillation criteria based on a new weighted function for linear matrix Hamiltonian systems and the existences of the positive solutions or nontrivial solutions of nonlinear differential equations.

## Applications of Symmetries for Solutions of Einstein Equations

General relativity is a physical theory which nowadays plays a key role in astrophysics and in physics and in this way it is important for a number of ambitious experiments and space missions. Einstein equations are central piece of general relativity. Einstein equations are expressed in terms of coupled system of highly nonlinear partial differential equations describing the matter content of space-time. The present work is to give an exposition of parts of the theory of partial differential equations that are needed in this subject and to represent exact solutions to Einstein equations. This book deals with various system of non linear partial differential equations corresponding to the Einstein equations for non diagonal Einstein-Rosen Metrics, Cylindrically Symmetric Null Fields, Vacuum Field Equations etc. from the view point of underlying symmetries and then to obtain their some new explicit exact solutions by using symmetry techniques like Lie symmetry analysis, symmetry reduction etc. These exact solutions play a significant for understanding of various phenomenons and are utilized for checking validity of numerical and approximation techniques and programs.

## Improved Tanh and Sech Methods for Obtaining New Exact Solutions

Exact solutions to nonlinear evolution equations (NEEs) play an important role in nonlinear physical science, since the characteristics of these solutions may well simulate real-life physical phenomena. One of the benefits of finding new exact solutions to such nonlinear partial differential equations (PDEs) is to give a better understanding on the various characteristics of the solutions. The main task of this work is to show that our proposed methods, improved tanh and sech methods, are very efficient in solving various types of NEEs and PDEs including special equations than using classical tanh and sech methods. This efficiency is because of their rich with the multiple traveling wave solutions than classical tanh and sech methods. From the obtained results, we can not only recover the previous solutions obtained by some authors but also obtain some new and more general solitary wave, singular solitary wave and periodic solutions. Illustrating the theory of nonlinear transmission lines (NLTLs), showing the ability of NLTL to generate solitons and solving the model equation of NLTL in presence of loss are other tasks of this book.

## Albert C. J. Luo Analytical Routes to Chaos in Nonlinear Engineering

Nonlinear problems are of interest to engineers, physicists and mathematicians and many other scientists because most systems are inherently nonlinear in nature. As nonlinear equations are difficult to solve, nonlinear systems are commonly approximated by linear equations. This works well up to some accuracy and some range for the input values, but some interesting phenomena such as chaos and singularities are hidden by linearization and perturbation analysis. It follows that some aspects of the behavior of a nonlinear system appear commonly to be chaotic, unpredictable or counterintuitive. Although such a chaotic behavior may resemble a random behavior, it is absolutely deterministic. Analytical Routes to Chaos in Nonlinear Engineering discusses analytical solutions of periodic motions to chaos or quasi-periodic motions in nonlinear dynamical systems in engineering and considers engineering applications, design, and control. It systematically discusses complex nonlinear phenomena in engineering nonlinear systems, including the periodically forced Duffing oscillator, nonlinear self-excited systems, nonlinear parametric systems and nonlinear rotor systems. Nonlinear models used in engineering are also presented and a brief history of the topic is provided. Key features: Considers engineering applications, design and control Presents analytical techniques to show how to find the periodic motions to chaos in nonlinear dynamical systems Systematically discusses complex nonlinear phenomena in engineering nonlinear systems Presents extensively used nonlinear models in engineering Analytical Routes to Chaos in Nonlinear Engineering is a practical reference for researchers and practitioners across engineering, mathematics and physics disciplines, and is also a useful source of information for graduate and senior undergraduate students in these areas.

## Periodic solutions of a certain non-linear differential equations

The study of nonlinear oscillators equations is of great importance not only in all areas of physics but also in engineering and other disciplines, since most phenomena in our word are nonlinear and are described by nonlinear equations. Recently, considerable attention has been direct towards the analytical solutions for nonlinear oscillators, for example, elliptic homotopy averaging method, amplitude-frequency formulation, homotopy perturbation method, parameter-expanding method, energy balance method, and others. The aim of this thesis is to study the periodic solutions for some physical systems which the mathematical formulation of these systems leads to a certain set of nonlinear ordinary differential equations of the second order.

## Equivariant Degree with Symmetric Nonlinear Boundary Value Problems

The Boundary value/periodic problems for the nonlinear equation (or, more generally, second order nonlinear ODEs) have been the focus of nonlinear analysis study for a long time. The goal of this book is to show how the equivariant degree theory can be used for the systematic study of multiple solutions to several (symmetric) generalizations of BVP and for the classification of symmetric properties of these solutions. There are several classical methods of nonlinear analysis used to solve the BVP. However, their application encounters serious difficulties if: the group of symmetries is large, the dimension of the problem is high, and multiplicities of eigenvalues of linearizations are large, etc. In this book, we: (i) set up the abstract functional analysis framework for studying symmetric properties of multiple solutions to symmetric generalizations of the BV problem via the equivariant degree approach; (ii) describe wide classes of second order BVPs admitting dihedral symmetries to which the abstract theory can be effectively applied; (iii) and apply the obtained results to several classes of implicit second order symmetric differential equations.

## Maximum Principle and Existence of Weak Solutions

In this book, we study the validity of the maximum principle (one of the most useful and best known tools employed in the study of partial differential equations) for some nonlinear elliptic systems, with variable coefficients, involving the weighted p-Laplcaian operators on bounded and unbounded domains. Also, using a different methods like the nonlinear theory of monotone operators, subsuper solutions method and an approximation (perturbation) method, we study the existence of positive weak solutions for some nonlinear elliptic systems, with variable coefficients, involving the weighted p-Laplcaian operators on bounded and unbounded domains.

## Analysis of the SDE/Monte Carlo Approach in Studying Nonlinear Systems

The reader is about to embark on a tutorial journey through a series of nonlinear dynamic systems that contain a rich tapestry of phenomena and solutions. The study of nonlinear systems can be greatly enhanced by the combined use of the stochastic dynamic equations and Monte Carlo calculations. When a dynamic system is forced and dissipative all the trajectories tend toward a bounded set of zero volume - often a strange attractor with a fractal dimension. The stochastic dynamic equations can directly reveal the statistical moments of the system, but their direct solution is inefficient, and they are not a closed set. The power of the combined method is that the time averaged Monte Carlo moments will agree exactly with equations described by the left hand side of the full stochastic dynamic equations set to zero - no closure is required. Every equation expresses an exact relationship among the variables. One is able to delve far deeper into the nature of the nonlinear systems. This tutorial exposition offers the tools for the past nonlinear modeling efforts in the traditional physical sciences and in various complex modeling problems in new fields of biology and health sciences.

## Moving Excitations Through A Reaction-Diffusion System

This book focuses on exact construction of moving excitations in nonlinear dissipative lattice systems. The lattice structure arises from the interaction among units discretely distributed in space where each unit follows a nonlinear evolution dynamics. The class of systems we consider includes Nagumo and FitzHugh-Nagumo (FHN) type pde’s. In each of these we replace the commonly considered cubic nonlinearity with an appropriate piecewise linear one. This reduces the problem of exact construction of the moving excitations to one of constructing the general solution of a linear evolution equation in terms of the eigenmodes in appropriate intervals of the relevant propagation variable and a matching of the solutions across those intervals. As solutions of discrete Nagumo model we construct two classes of fronts: kink and antikink, which are related through a symmetry transformation. The solutions to discrete FHN systems are the pulse and pulse-trains constructed on the basis of singular perturbation technique where a conjugate pair of kink and antikink form the leading and trailing edges of the pulse, the two being joined up through the slow evolution of a recovery variable.

## Powerful Methods for Solving Nonlinear evolution Equations

It is well known that nonlinear evolution equations (NLEEs) are widely used to describe physical phenomena in various scientific and engineering fields, such as fluid mechanics, plasma physics, optical fibers, biology, solid state physics, etc. In order to understand the mechanisms of those physical phenomena, it is necessary to explore their solutions and properties. Solutions for the NLEEs can not only describe the designated problems, but also give more insights on the physical aspects of the problems in the related fields. In recent years, various powerful methods have been presented for finding exact solutions of the NLEEs in mathematical physics. The main purpose of this book is to illustrate how to establish solitary and periodic solutions of many NLEEs. Many illustrative examples are discussed by different methods, enjoy reading it.

## Variational Iteration Method

Differential equations are encountered in various fields such as physics, chemistry, biology, mathematics and engineering. Most nonlinear models of real-life problems are still very difficult to solve either numerically or theoretically. Many unrealistic assumptions have to be made to make nonlinear models solvable. There has recently been much attention devoted to the search for better and more efficient solution methods for determining a solution, approximate or exact, analytical or numerical, to nonlinear models. Finding exact/approximate solutions of these nonlinear equations are interesting and important. One of these methods is variational iteration method (VIM), which has been proposed by Ji-Huan He in 1997 based on the general Lagrange’s multiplier method. The main feature of the method is that the solution of the linearized problem is used as the initial approximation for the linear and nonlinear problems. Then a more highly precise approximation at some special point can be obtained. This approximation converges rapidly to an accurate solution. VIM is very powerful and efficient in finding analytical as well as numerical solutions for a wide class of differential equation