*Wednesday 19th April*–

*Wednesday 19th April 2023*

Organised in collaboration with the School of Mathematics, University of Bristol, UK

**Venue**: Lecture Theatre 2.41, School of Mathematics, Fry Building, Woodland Road, University of Bristol

**Title:*** Nodal count via topological data analysis*

**Abstract: ** A nodal domain of a function is a connected component of the complement to its zero set. The celebrated Courant nodal domain theorem implies that the number of nodal domains of a Laplace eigenfunction is controlled by the corresponding eigenvalue. There have been many attempts to find an appropriate generalization of this statement in various directions: to linear combinations of eigenfunctions, to their products, to other operators. It turns out that these and other extensions of Courant’s theorem can be obtained if one counts the nodal domains in a coarse way, i.e. ignoring small oscillations. The proof uses multiscale polynomial approximation in Sobolev spaces and the theory of persistence barcodes originating in topological data analysis. The talk is based on a joint work with L. Buhovsky, J. Payette, L. Polterovich, E. Shelukhin and V. Stojisavljević. No prior knowledge of spectral geometry and topological persistence will be assumed.

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