Quasilinearization method 4 Upper and lower solutions 4 Antimaximum principle 2 Boundary conditions 2 Convergence of numerical methods 2 Elliptic PDEs 2 Elliptic partial differential equations 2 Fourth order periodic problems 2 Iterative methods 2 Linearization 2 Nonlinear boundary conditions 2 Nonlinear equations 2 Partial differential equations 2