Hilbert space Operator theory 5 Differential equations 4 Invariant subspaces 4 Banach spaces 3 Differential equations, Partial 3 Linear operators 3 Banach algebras 2 Convex functions 2 Convex programming 2 Differential operators 2 Dirichlet principle 2 Dirichlet-Raum 2 Holomorphic functions 2 Mathematics 2 Problems, exercises, etc 2 Approximation theory 1 Bessel funtions 1 C*-algebras 1 Chemistry, Physical and theoretical 1 Eigenvectors 1 Fixed point theory 1 Functional analysis 1 Functions of complex variables 1 Gaussian processes 1 Generalized inverses 1 Inner product spaces 1 Integral equations 1 Iterative methods (Mathematics) 1 Kernel functions 1