Boundary value problems Differential equations, Nonlinear 3 Numerical solutions 3 Calculus of variations 2 Differential equations, Elliptic 2 Differential equations, Partial 2 Fourier series 2 mer ... Differential equations 1 Differential equations, Hyperbolic 1 Green's functions 1 Hilbert space 1 Mathematical physics 1 Pseudodifferential operators 1 Variational principles 1 Wave equation 1 mindre ...