# MA3G7 Functional Analysis I

**Lecturer:** Jan Grebik

**Term(s):** Term 1

**Status for Mathematics students:** List A

**Commitment:** 30 lectures

**Assessment: **100% exam

**Formal registration prerequisites: **None

**Assumed knowledge: **

- MA244 Analysis III or MA258 Mathematical Analysis III
- MA260 Norms, Metrics, & Topologies or MA222 Metric Spaces

**Useful background:**

**Synergies: **

**Leads To: **The following modules have this module listed as **assumed knowledge** or **useful background:**

- MA3G8 Functional Analysis II
- MA427 Ergodic Theory
- MA433 Fourier Analysis
- MA4A7 Quantum Mechanics: Basic Principles and Probabilistic Methods
- MA4A2 Advanced Partial Differential Equations
- MA4J0 Advanced Real Analysis
- MA4L3 Large Deviation Theory
- MA4M2 Mathematics of Inverse Problems
- MA4L9 Variational Analysis and Evolution Equations

**Content**: This is essentially a module about infinite-dimensional Hilbert spaces, which arise naturally in many areas of applied mathematics. The ideas presented here allow for a rigorous understanding of Fourier series and more generally the theory of Sturm-Liouville boundary value problems. They also form the cornerstone of the modern theory of partial differential equations.

Hilbert spaces retain many of the familiar properties of finite-dimensional Euclidean spaces ( ) - in particular the inner product and the derived notions of length and distance - while requiring an infinite number of basis elements. The fact that the spaces are infinite-dimensional introduces new possibilities, and much of the theory is devoted to reasserting control over these under suitable conditions.

The module falls, roughly, into three parts. In the first we will introduce Hilbert spaces via a number of canonical examples, and investigate the geometric parallels with Euclidean spaces (inner product, expansion in terms of basis elements, etc.). We will then consider various different notions of convergence in a Hilbert space, which although equivalent in finite-dimensional spaces differ in this context. Finally we consider properties of linear operators between Hilbert spaces (corresponding to the theory of matrices between finite-dimensional spaces), in particular recovering for a special class of such operators (compact self-adjoint operators) very similar results to those available in the finite-dimensional setting.

Throughout the abstract theory will be motivated and illustrated by more concrete examples.

**Books**: An obvious recommendation would be:

JC Robinson, *An Introduction to Functional Analysis, *Cambridge University Press, 2020.

The module will follow parts of this book quite closely. However, if you want a different take on the material,

the book BP Rynne & MA Youngson, *Linear Functional Analysis*, Springer-Verlag, London, 2000 is very good.