Conjectured Kolmogorov-number lower bound for quasi-Banach Schatten embeddings

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Let SpNS_p^N and SqNS_q^N be Schatten classes of N×NN\times N matrices, and let dnd_n denote the nnth Kolmogorov number of the embedding. For 0<p≤∞0<p\leq\infty, 0<q≤10<q\leq1, q≤pq\leq p, and n,N∈Nn,N\in\mathbb N satisfying 1≤n≤N21\leq n\leq N^2, the quasi-Banach Kolmogorov-number conjecture. One has

dn(SpN↪SqN)≳p,qmax⁡{1,N2−n+1N}1/q−1/p.d_n\big(\mathcal{S}_p^N\hookrightarrow\mathcal{S}_q^N\big)\gtrsim_{p,q}\max\left\{1,\frac{N^2-n+1}{N}\right\}^{1/q-1/p}.

The conjecture concerns Kolmogorov numbers when the codomain is a quasi-Banach Schatten space; the source gives no resolution.

References

Primary source

Joscha Prochno and Michał Strzelecki, “Approximation, Gelfand, and Kolmogorov numbers of Schatten class embeddings”, arXiv:2103.13050 (2021).

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