Uniform interpolation-error conjecture for self-conjugate grids

From papers

Let II be the interpolation interval, let D\mathbb{D} be the unit disc, let En(D)\mathscr{E}_n(\mathbb{D}) be the entire functions g:CCg:\mathbb{C}\to\mathbb{C} satisfying g(n)D1\|g^{(n)}\|_{\mathbb{D}}\leqslant1, and let z1:nDnz_{1:n}\in\mathbb{D}^n be a self-conjugate grid. 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 uniform conjecture. For every 0kn10\leqslant k\leqslant n-1,

supgEn(D)g(k)()g^(k)(z1:n)I=1n!f(k)(z1:n)I.\operatorname{\mathsf{\sup}}_{g\in\mathscr{E}_n(\mathbb{D})}\|g^{(k)}(\cdot)-\hat g^{(k)}(\cdot\mid z_{1:n})\|_I=\frac{1}{n!}\|f^{(k)}(\cdot\mid z_{1:n})\|_I.

Equivalently, the source gives the corresponding supremum identity involving Schur polynomials. This would generalize the real-node result of Kallioniemi and Shadrin to self-conjugate grids in the unit disc; the source does not provide a resolution.

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Sources & referencesView supporting material

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).

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