Variational Principles and Free-boundary Problems 
Avner Friedman
John Wiley & Sons
This advanced graduate-level text examines variational methods in partial differential equations and illustrates their applications to a number of free-boundary problems. Detailed statements of the standard theory of elliptic and parabolic operators make this treatment readable for engineers, students, and nonspecialists alike. Each chapter concludes with several problems and exercises.1982 edition.