28.11.2024 (Thursday)

Daniel Seco (Universidad de La Laguna)
28 Nov at 11:00 - 12:00
KCL, Strand - S5.20

We give an example of a function $f$ non-vanishing in the closed bidisk and the affine polynomial minimizing the norm of $1-pf$ in the Hardy space of the bidisk among all affine polynomials $p$. We show that this polynomial vanishes inside the bidisk. This provides a counterexample to the weakest form of a conjecture due to Shanks that has been open since 1980, with applications that arose from digital filter design. This counterexample has a simple form and follows naturally from previous work, where the phenomenon of zeros seeping into the unit disk was already observed for similar minimization problems in one variable.

Posted by felipe.marceca@kcl.ac.uk