Spectral theory (Mathematics) 58 Differential operators 5 Differential equations, Partial 4 Operator theory 4 Boundary value problems 3 Eigenvalues 3 Elliptic operators 3 Evolution equations, Nonlinear 3 Linear operators 3 Schrodinger operator 3 Signal processing 3 Solitons 3 Asymptotic expansions 2 Automorphic forms 2 Banach spaces 2 Data processing 2 Decomposition (Mathematics) 2 Differential equations, Elliptic 2 Finite element method 2 Functions, Zeta 2 Hilbert space 2 Mathematical physics 2 Number theory 2 Numerical solutions 2 Pseudodifferential operators 2 Random operators 2 Scattering (Mathematics) 2 Sequences (Mathematics) 2 Almost periodic operators 1 Analytic functions 1