English

Normal operators with highly incompatible off-diagonal corners

Functional Analysis 2019-08-21 v1

Abstract

Let H\mathcal{H} be a complex, separable Hilbert space, and B(H)\mathcal{B}(\mathcal{H}) denote the set of all bounded linear operators on H\mathcal{H}. Given an orthogonal projection PB(H)P \in \mathcal{B}(\mathcal{H}) and an operator DB(H)D \in \mathcal{B}(\mathcal{H}), we may write D=[D1D2D3D4]D=\begin{bmatrix} D_1& D_2 D_3 & D_4 \end{bmatrix} relative to the decomposition H=ranPran(IP)\mathcal{H} = \mathrm{ran}\, P \oplus \mathrm{ran}\, (I-P). In this paper we study the question: for which non-negative integers j,kj, k can we find a normal operator DD and an orthogonal projection PP such that rankD2=j\mathrm{rank}\, D_2 = j and rankD3=k\mathrm{rank}\, D_3 = k? Complete results are obtained in the case where dimH<\mathrm{dim}\, \mathcal{H} < \infty, and partial results are obtained in the infinite-dimensional setting.

Keywords

Cite

@article{arxiv.1908.07024,
  title  = {Normal operators with highly incompatible off-diagonal corners},
  author = {Laurent W. Marcoux and Heydar Radjavi and Yuanhang Zhang},
  journal= {arXiv preprint arXiv:1908.07024},
  year   = {2019}
}

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submitted

R2 v1 2026-06-23T10:51:28.415Z