**Minicourse «Gabor analysis for rational functions»**

St. Petersburg State University and Euler International Mathematical Institute are happy to announce a new minicourse, headed by **Yurii S. Belov.** Lectures scheduled to Wednesdays starting 14 April, 7pm. To attend the lectures, please join zoom channel 511-327-649. If you do not know the password, please write an email to Yurii Belov. Video records of the course are available here.

**Course description**

This series of lectures is aimed to present a recent progress in Gabor analysis for rational functions and is based on the works by A. Kulikov, Yu. Lyubarskii and the author. Given a function we call a collection of time-frequency shifts of ,

a Gabor system.

Gabor systems constitute one of the most important and natural objects in modern signal analysis, and they have numerous applications in quantum mechanics

and mathematical physics. Such a system provides a natural representation of a given signal in terms of its samples in the sense of classical Fourier analysis.

To produce a stable reconstruction of an arbitrary function by its {\it Gabor samples }

we require for the corresponding Gabor system to be a {\it a frame}. One of the main questions of Gabor analysis is to describe all rectangular lattices which generate a Gabor frame in for

a given function .

The complete answer is known only in a select few cases ( being Gaussian, one-sided exponential etc.) We start by giving an exposition of classical results by Daubechies, Grossman, Seip, Janssen, Grochenig and others. Then we develop a thorough investigation (featuring complete proofs) of frames generated by rational functions. Finally we prove the results about irregular sampling for Cauchy kernel (simplest rational function from ).

**Program:**

- Gabor systems: what they are, how do they appear and why we need them. %Overview.
- Main criterion for rational functions. Finite-diagonal matrices.
- Hunting for positivity. Herglotz functions.
- Irrational densities. Daubechies conjecture.
- Near the criticial hyperbola. Large densities.
- Irregular sampling. Toeplitz approach.
- Sum of two Cauchy kernels. Estimates of frame bounds.

This course is accessible to second year students. The prerequisites are: basic complex analysis and linear algebra.

Everyone is welcome!

Lecture 1. Notes

Lecture 2. Notes

Lecture 3. Notes

Lecture 4. Notes

Lecture 5. Notes