Zero-freeness conjecture for optimal polynomial approximants in Hardy spaces

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Let 1<p<∞1<p<\infty, f∈Hpf\in H^p, and n∈Nn\in\mathbb{N}. If f(0)≠0f(0)\neq 0, then the optimal polynomial approximant qn,p[f,1]q_{n,p}[f,1] is the polynomial of degree at most nn that best approximates 1/f1/f in the relevant LpL^p setting, and it is zero-free in the closed unit disk D‾\overline{\mathbb{D}}. Zero-freeness conjecture. For every such ff, qn,p[f,1]q_{n,p}[f,1] is zero-free in D‾\overline{\mathbb{D}}. This conjecture extends the zero-location phenomena known for least-squares and Shanks-type approximants to the broader range 1<p<∞1<p<\infty in Hardy spaces; its general validity remains open.

References

Primary source

Raymond Centner, “Optimal Polynomial Approximants in L^p”, arXiv:2112.14002 (2022).

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