Perturbations Of The Point, Residual And Continuous Spectrum Of3×3Upper Triangular Operator Matrices

In this thesis, the perturbations of the point, residual and continuous spectrum of3×3upper triangular operator matrices are investigated. Similarly, the perturbations of1,2-type point and residual spectrum are also considered. By using the analysis method and block operator technique, the complete descriptions of the preceding perturbations are given.