Linear operators Banach algebras 4 Spectral theory (Mathematics) 4 Banach spaces 2 Congresses 2 Hilbert space 2 Linear topological spaces 2 Normed linear spaces 2 Perturbation (Mathematics) 2 Approximation theory 1 Continuity 1 Differential equations 1 Equations 1 Frechet spaces 1 Function spaces 1 Generalized inverses 1 Hamiltonian operator 1 Lattice theory 1 Locally convex spaces 1 Matrices 1 Matrix inversion 1 Nonlinear theories 1 Nuclear spaces (Functional analysis) 1 Numerical solutions 1 Operator theory 1 Oscillations 1 Positive operators 1 Pseudodifferential operators 1 System analysis 1 Tensor products 1