This book uses techniques of Fourier series and functional analysis to deal with certain problems in differential equations. The Fourier series and functional analysis are merely tools; the authors' real interest lies in the differential equations that they study. It has been known since 1967 that a wide variety of sets {e wikt } of complex exponential functions play an important role in the control theory of systems governed by partial differential equations. However, this book is the first serious attempt to gather all of the available theory of these "nonharmonic Fourier series" in one place, combining published results with new results by the authors, to create a unique source of such material for practicing applied mathematicians, engineers and other scientific professionals.

First serious attempt to gather all of the available theory of "nonharmonic Fourier series" in one place, combining published results with new results by the authors

Autorentext

Vilmos Komornik has studied in Budapest, Hungary, and has taught in Hungary and France for nearly 40 years. His main research fields are control theory of partial differential equations and combinatorial number theory. He has made a number of contributions to the theory of J.L. Lions on exact controllability and stabilization and has co-authored several papers on expansions in noninteger bases with P. Erd s. He is an external member of the Hungarian Academy of Sciences.

Inhalt
Observation, Control, and Stabilization.- Well-Posedness in a Riesz Basis Setting.- Observability of Strings.- Observability of Beams.- Vector Sum Estimates.- Problems on Spherical Domains.- Multidimensional Ingham-Type Theorems.- A General Ingham-Type Theorem.- Problems with Weakened Gap Conditions.