Nonlinear functional analysis is an important branch of contemporary
mathematics. It's related to topology, ordinary differential equations,
partial differential equations, groups, dynamical systems, differential
geometry, measure theory, and more. In this book, the author presents
some new and interesting results on fundamental methods in nonlinear
functional analysis, namely variational, topological and partial order
methods, which have been used extensively to solve existence of
solutions for elliptic equations, wave equations, Schrödinger equations,
Hamiltonian systems etc., and are also used to study the existence of
multiple solutions and properties of solutions. This book is useful for
researchers and graduate students in the field of nonlinear functional
analysis.