On the Perturbation of the Spectra of Kato Upper Triangular Operator Matrices
Tian Junhong, Xiaohong Cao · Advances in Mathematics · 2012
Letσ_2(A) =σ_e(A)∪σ_k(A) U{λ∈C:ind(A-λI) 0},whereσ_e(A) andσ_k(A) denote the essential spectrum and Kato spectrum of an operator A,respectively.In thispaper,using the relation between the nullity and the defect of a given pair operators,we studythe perturbation of the spectrumσ_2(-) for upper triangular operator matrices.