Spectral theory (Mathematics) Operator theory 10 Differential equations, Partial 5 Linear operators 4 Mathematical physics 4 Perturbation (Mathematics) 4 Schrödinger operator 4 more ... Boundary value problems 3 Eigenvalues 3 Number theory 3 Numerical solutions 3 Quantum theory 3 Banach algebras 2 Banach spaces 2 Differentiable dynamical systems 2 Differential equations 2 Differential operators 2 Graph theory 2 Harmonic analysis 2 Mathematical models 2 Mathematics 2 Numerical analysis 2 Scattering (Mathematics) 2 Sequences (Mathematics) 2 Structural analysis (Engineering) 2 Wave-motion, Theory of 2 Analytic functions 1 Anisotropy 1 Approximation methods 1 Approximation theory 1 less ...