Higher rank numerical ranges of normal matrices

Hwa Long Gau, Chi Kwong Li, Yiu Tung Poon, Nung Sing Sze

Research output: Journal article publicationJournal articleAcademic researchpeer-review

15 Citations (Scopus)


The higher rank numerical range is closely connected to the construction of quantum error correction code for a noisy quantum channel. It is known that if a normal matrix A ε Mn has eigenvalues a1, ⋯ , an, then its higher rank numerical range Γκ(A) is the intersection of convex polygons with vertices aj1, ⋯ , ajn-k+1, where 1 ≤ j1< ⋯ ≤ jn-k+1≤ n. In this paper, it is shown that the higher rank numerical range of a normal matrix with m distinct eigenvalues can be written as the intersection of no more than max{m, 4} closed half planes. In addition, given a convex polygon P, a construction is given for a normal matrix A ε Mnwith minimum n such that Δκ(A) = P. In particular, if P has p vertices, with p ≥ 3, there is a normal matrix A ε Mnwith n ≤ max {p + k -1, 2k + 2} such that Γκ(A) = P.
Original languageEnglish
Pages (from-to)23-43
Number of pages21
JournalSIAM Journal on Matrix Analysis and Applications
Issue number1
Publication statusPublished - 14 Mar 2011


  • Convex polygon
  • Higher rank numerical range
  • Normal matrices
  • Quantum error correction

ASJC Scopus subject areas

  • Analysis

Cite this