There are no prerequisites.

# Operator theory

• Compact operators on Banach spaces, ascent and descent of an operator, Riesz decomposition and spectral theory of compact operators

• Invariant subspaces, Schauder's fixed point theorem, Lomonosov's theorem and consequences, triangularizability of compact operators

• Fredholm operators and their index, the index theorem, Atkinson's perturbation theorems, Calkin algebra and essential spectrum, polynomially compact operators

• Banach algebras, Riesz functional calculus, dependence of the spectrum on the algebra, isolated points of the spectrum and Laurent series expansion of the resolvent, essential spectrum and Riesz operators, essential spectral radius

• Additional topic: strictly singular operators, example of a strictly singular non-compact operator, Kato's characterization of strictly singular operators, spectral theory of strictly singular operators

• Additional topic: Schauder basis of a Banach space and basic sequences, examples of spaces with Schauder basis, classical sequence spaces, approximation property, density of finite-rank operators in compact operators

- Y. A. Abramovich, C. D. Aliprantis: An invitation to operator theory, Providence : American Mathematical Society, cop. 2002.
- Y. A. Abramovich, C. D. Aliprantis: Problems in operator theory, Providence : American Mathematical Society, cop. 2002.
- F. Albiac, N. J. Kalton: Topics in Banach space theory, New York : Springer, cop. 2006.
- J. B. Conway: A Course in functional analysis, 2nd ed. - New York : Springer, cop. 1990.
- I. Gohberg, S. Goldberg, M. A. Kaashoek: Classes of linear operators. Vol. 1, Basel : Birkhäuser, 1990.
- G. K. Pedersen: Analysis now, New York : Springer, cop. 1989.
- H. Radjavi, P. Rosenthal: Simultaneous triangularization, New York : Springer, 2000.
- I. Vidav: Linearni operatorji v Banachovih prostorih, Ljubljana : Društvo matematikov, fizikov in astronomov SR Slovenije, 1982.

Treatment of some classes of bounded linear operators on Hilbert and Banach spaces.

Knowledge and understanding: Knowledge of some classes of linear operators, the ability to apply the acquired knowledge.

Application: Operator theory is used in natural sciences and other areas of science such as economics.

Reflection: Understanding of the theory, strengthened by examples.

Transferable skills: Identifying and solving problems. Ability to use a wide range of references.

Lectures, exercises, homeworks, consultations

Homeworks and theoretical exam

Roman Drnovšek:

DRNOVŠEK, Roman. Common invariant subspaces for collections of operators. Integral equations and operator theory, ISSN 0378-620X, 2001, vol. 39, no. 3, str. 253-266. [COBISS-SI-ID 10597721]

DRNOVŠEK, Roman. A generalization of Levinger's theorem to positive kernel operators. Glasgow mathematical journal, ISSN 0017-0895, 2003, vol. 45, part 3, str. 545-555. [COBISS-SI-ID 12825945]

DRNOVŠEK, Roman. Invariant subspaces for operator semigroups with commutators of rank at most one. Journal of functional analysis, ISSN 0022-1236, 2009, vol. 256, iss. 12, str. 4187-4196. [COBISS-SI-ID 15167321]

Marko Kandić:

KANDIĆ, Marko. On algebras of polynomially compact operators. Linear and Multilinear Algebra, ISSN 0308-1087, 2016, vol. 64, no. 6, str. 1185-1196. [COBISS-SI-ID 17493337]

KANDIĆ, Marko. Ideal-triangularizability of nil-algebras generated by positive operators. Proceedings of the American Mathematical Society, ISSN 0002-9939, 2011, vol. 139, no. 2, str. 485-490. [COBISS-SI-ID 15710809]

DRNOVŠEK, Roman, KANDIĆ, Marko. Positive operators as commutators of positive operators. Studia Mathematica, ISSN 0039-3223, 2019, tom 245, str. 185-200. [COBISS-SI-ID 18407769]