Upper and lower solutions Boundary-value problem on the half line 4 Diagonal argument 4 Neumann conditions 4 Quasilinearization method 4 Antimaximum principle 2 Boundary conditions 2 Brownian movement 2 Convergence of numerical methods 2 Differential equations 2 Elliptic PDEs 2 Elliptic partial differential equations 2 Financial market 2 Fourth order periodic problems 2 Harmonic analysis 2 Integro-differential operator 2 Iterative methods 2 Levy model 2 Linearization 2 Mathematical operators 2 Nonlinear boundary conditions 2 Nonlinear equations 2 Partial differential equations 2 Spherical harmonics 2