An Introduction to Functional Analysis

This accessible text covers key results in functional analysis that are essential for further study in the calculus of variations, analysis, dynamical systems, and the theory of partial differential equations. The treatment of Hilbert spaces covers the topics required to prove the Hilbert?Schmidt theorem, including orthonormal bases, the Riesz representation theorem, and the basics of spectral theory. The material on Banach spaces and their duals includes the Hahn?Banach theorem, the Krein?Milman theorem, and results based on the Baire category theorem, before culminating in a proof of sequential weak compactness in reflexive spaces. Arguments are presented in detail, and more than 200 fully-worked exercises are included to provide practice applying techniques and ideas beyond the major theorems. Familiarity with the basic theory of vector spaces and point-set topology is assumed, but knowledge of measure theory is not required, making this book ideal for upper undergraduate-level and beginning graduate-level courses.

Part I. Preliminaries: 1. Vector spaces and bases; 2. Metric spaces; Part II. Normed Linear Spaces: 3. Norms and normed spaces; 4. Complete normed spaces; 5. Finite-dimensional normed spaces; 6. Spaces of continuous functions; 7. Completions and the Lebesgue spaces Lp(Ω); Part III. Hilbert Spaces: 8. Hilbert spaces; 9. Orthonormal sets and orthonormal bases for Hilbert spaces; 10. Closest points and approximation; 11. Linear maps between normed spaces; 12. Dual spaces and the Riesz representation theorem; 13. The Hilbert adjoint of a linear operator; 14. The spectrum of a bounded linear operator; 15. Compact linear operators; 16. The Hilbert–Schmidt theorem; 17. Application: Sturm–Liouville problems; Part IV. Banach Spaces: 18. Dual spaces of Banach spaces; 19. The Hahn–Banach theorem; 20. Some applications of the Hahn–Banach theorem; 21. Convex subsets of Banach spaces; 22. The principle of uniform boundedness; 23. The open mapping, inverse mapping, and closed graph theorems; 24. Spectral theory for compact operators; 25. Unbounded operators on Hilbert spaces; 26. Reflexive spaces; 27. Weak and weak-* convergence; Appendix A. Zorn's lemma; Appendix B. Lebesgue integration; Appendix C. The Banach–Alaoglu theorem; Solutions to exercises; References; Index.

James C. Robinson is a professor in the Mathematics Institute at the University of Warwick. He has been the recipient of a Royal Society University Research Fellowship and an Engineering and Physical Sciences Research Council (EPSRC) Leadership Fellowship. He has written six books in addition to his many publications in infinite-dimensional dynamical systems, dimension theory, and partial differential equations.