Nonlinear equations Mathematical models 22 Boundary conditions 18 Problem solving 18 Differential equations 16 Laplace transforms 16 Approximation theory 14 Laplace equation 12 Nonlinear boundary conditions 12 Theorem proving 12 Nonlinear systems 10 Optimization 10 Schrodinger equation 10 Convergence of numerical methods 8 Integrodifferential equations 8 Lithospheric 8 Nonlinear differential equation 8 Partial differential equations 8 Two-layer systems 8 Upper mantle 8 Viscosity 8 Differentiation (calculus) 6 Ionization 6 Iterative methods 6 Mathematical operators 6 Metal surfaces 6 Numerical methods 6 Optimization problems 6 P-Laplace operator 6 P-Laplacian 6