2010/04/21 by Gaaya, Haykel · 1 citation
#FOS: Mathematics #Functional Analysis (math.FA)
paper · doi:10.48550/arxiv.1004.3751
For any n-by-n complex matrix T and any 1\leqslant k\leqslant n, let Λk(T) the set of all λ∈ \C such that PTP=λP for some rank-k orthogonal projection P be its higher rank-k numerical range. It is shown that if \bbS is the n-dimensional shift on \Cn then its rank-k numerical range is the circular disc centred in zero and with radius cos\dfrackπn+1 if 1