28.11.2024 (Thursday)

AN A counterexample to the Weak Shanks Conjecture

regular seminar Daniel Seco (Universidad de La Laguna)

at:
11:00 - 12:00
KCL, Strand
room: S5.20
abstract:

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.

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