# Coincidence and Calculation of some Strict $s$-Numbers

### David E. Edmunds

University of Sussex, Brighton, United Kingdom### Jan Lang

Ohio State University, Columbus, USA

## Abstract

The paper considers the so-called strict $s$-numbers, which form an important subclass of the family of all $s$-numbers. For operators acting between Hilbert spaces the various $s$-numbers are known to coincide: here we give examples of linear maps $T$ and non-Hilbert spaces $X, Y$ such that all strict $s$-numbers of $T : X \to Y$ coincide. The maps considered are either simple integral operators acting in Lebesgue spaces or Sobolev embeddings; in these cases the exact value of the strict $s$-numbers is determined.

## Cite this article

David E. Edmunds, Jan Lang, Coincidence and Calculation of some Strict $s$-Numbers. Z. Anal. Anwend. 31 (2012), no. 2, pp. 161–181

DOI 10.4171/ZAA/1453