Hilbert space 50 Fourier transform-- Hilbert transform-- Laplace transform-- Integral transform 31 Operator theory 7 Differential equations 4 Invariant subspaces 4 Mathematics 4 Banach spaces 3 Differential equations, Partial 3 Functional analysis 3 Linear operators 3 Banach algebras 2 Convex functions 2 Convex programming 2 Differential operators 2 Dirichlet principle 2 Dirichlet-Raum 2 Hilbert algebras 2 Holomorphic functions 2 Problems, exercises, etc 2 Signal processing 2 Approximation theory 1 Bases (Linear topological spaces) 1 Bessel funtions 1 C*-algebras 1 Chemistry, Physical and theoretical 1 Decomposition (Mathematics) 1 Eigenvectors 1 Fixed point theory 1 Forms, Modular 1 Frames (Vector analysis) 1