Martin Schechter – författare

Since the birth of the calculus of variations, researchers have discovered that variational methods, when they apply, can obtain better results than most other methods. Moreover, they apply in a very large number of situations. It was realized many years ago that the solutions of a great number of problems are in effect critical points of functionals. Critical Point Theory and Its Applications presents some of the latest research in the area of critical point theory. Researchers have obtained many new results recently using this approach, and in most cases comparable results have not been obtained with other methods. This book describes the methods and presents the newest applications.

The topics covered in the book include extrema, even valued functionals, weak and double linking, sign changing solutions, Morse inequalities, and cohomology groups. The applications described include Hamiltonian systems, Schrödinger equations and systems, jumping nonlinearities, elliptic equations and systems, superlinear problems and beam equations. Many minimax theorems are established without the use of the (PS) compactness condition.

Many problems in science and engineering involve the solution of differential equations or systems. One of most successful methods of solving nonlinear equations is the determination of critical points of corresponding functionals. The study of critical points has grown rapidly in recent years and has led to new applications in other scientific disciplines. This monograph continues this theme and studies new results discovered since the author''s preceding book entitled Linking Methods in Critical Point Theory.

Written in a clear, sequential exposition, topics include semilinear problems, Fucik spectrum, multidimensional nonlinear wave equations, elliptic systems, and sandwich pairs, among others. With numerous examples and applications, this book explains the fundamental importance of minimax systems and describes how linking methods fit into the framework.

Minimax Systems and Critical Point Theory is accessible to graduate students with some background in functional analysis, and the new material makes this book a useful reference for researchers and mathematicians.

Review of the author''s previous Birkhäuser work, Linking Methods in Critical Point Theory:

The applications of the abstract theory are to the existence of (nontrivial) weak solutions of semilinear elliptic boundary value problems for partial differential equations, written in the form Au = f(x, u). . . . The author essentially shows how his methods can be applied whenever the nonlinearity has sublinear growth, and the associated functional may increase at a certain rate in every direction of the underlying space. This provides an elementary approach to such problems. . . . A clear overview of the contents of the book is presented in the first chapter, while bibliographical comments and variant results are described in the last one. -MathSciNet