Nung-Sing Sze

activity

20072026

most citedCanonical forms, higher rank numerical range, convexity, totally isotropic subspace, matrix equations

84 citations · 379 across the 37 of their papers we have counts for

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Showing 2007Show all

3 papers · 1 filter

math.FA2007★ 34 cited

Higher rank numerical ranges and low rank perturbations of quantum channels

Chi-Kwong Li, Yiu-Tung Poon, Nung-Sing Sze

For a positive integer $k$ , the rank- $k$ numerical range $Λ_{k} (A)$ of an operator $A$ acting on a Hilbert space $\cH$ of dimension at least $k$ is the set of scalars $λ$ such that $…

math.FA2007★ 38 cited

Condition for the higher rank numerical range to be non-empty

Chi-Kwong Li, Yiu-Tung Poon, Nung-Sing Sze

It is shown that the rank- $k$ numerical range of every $n$ -by- $n$ complex matrix is non-empty if $n \geq 3 k - 2$ . The proof is based on a recent characterization of the rank- $k$ num…

math.FA2007★ 84 cited

Canonical forms, higher rank numerical range, convexity, totally isotropic subspace, matrix equations

Chi-Kwong Li, Nung-Sing Sze

Results on matrix canonical forms are used to give a complete description of the higher rank numerical range of matrices arising from the study of quantum error correction. It is s…