On Perturbation of Operators and Rayleigh-Schrödinger Coefficients
Let A and E be self-adjoint matrices or operators on ℓ2(N), where A is fixed and E is a small perturbation. We study how the eigenvalues of A+E depend on E, with the aim of obtaining second order formulas that are explicitly computable in terms of the spectral decomposition of A and a certain block decomposition of E. In particular we extend the classical Rayleigh-Schrödinger formulas for the one-
