Critical Points of Functionals -- Minimax Systems -- Examples of Minimax Systems -- Ordinary Differential Equations -- The Method Using Flows -- Finding Linking Sets -- Sandwich Pairs -- Semilinear Problems -- Superlinear Problems -- Weak Linking -- Fučík Spectrum: Resonance -- Rotationally Invariant Solutions -- Semilinear Wave Equations -- Type (II) Regions -- Weak Sandwich Pairs -- Multiple Solutions -- Second-Order Periodic Systems.

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