Self-conjugate-grid pointwise interpolation-error conjecture

About 1 year old · traced to

Let D\mathbb{D} be the unit disc, let En(D)\mathscr{E}_n(\mathbb{D}) be the entire functions g:C→Cg:\mathbb{C}\to\mathbb{C} satisfying ∥g(n)∥D⩽1\|g^{(n)}\|_{\mathbb{D}}\leqslant1, and let z1:n∈Dnz_{1:n}\in\mathbb{D}^n be self-conjugate, meaning that nonreal nodes occur with their conjugates and every real node occurs with even multiplicity. Let f(⋅∣z1:n)f(\cdot\mid z_{1:n}) be the nodal polynomial and g^(⋅∣z1:n)\hat g(\cdot\mid z_{1:n}) the interpolation polynomial.

Self-conjugate-grid pointwise conjecture. For every 0⩽k⩽n−10\leqslant k\leqslant n-1,

sup⁡⁡g∈En(D)∣g(k)(z)−g^(k)(z∣z1:n)∣∣z=1=1n!∣f(k)(z∣z1:n)∣∣z=1.\left.\operatorname{\mathsf{\sup}}_{g\in\mathscr{E}_n(\mathbb{D})}|g^{(k)}(z)-\hat g^{(k)}(z\mid z_{1:n})|\right|_{z=1}=\left.\frac{1}{n!}|f^{(k)}(z\mid z_{1:n})|\right|_{z=1}.

If additionally Re⁡(z1:n)∈R+n\operatorname{\mathsf{Re}}(z_{1:n})\in\mathbb{R}^n_+, the same equality holds at z=0z=0. This is a proposed extension of the pointwise worst-case interpolation result from real nodes to self-conjugate grids; its resolution is not supplied in the source.

References

Primary source

Dmitrii M. Ostrovskii and Pavel S. Shcherbakov, “Amplitude maximization in stable systems, Schur positivity, and some conjectures on polynomial interpolation”, arXiv:2508.13554 (2025).

Progress summary

Never refreshed

Nothing recorded yet. Refresh searches the literature and the public web for attempts on this problem, and writes the first summary here.

Solutions 0

No solutions have been posted yet.