For the problems of interest here we shall only consider linear boundary conditions, which express a linear relation between the function and its partial derivatives. As before the maximal order of th...For the problems of interest here we shall only consider linear boundary conditions, which express a linear relation between the function and its partial derivatives. As before the maximal order of the derivative in the boundary condition is one order lower than the order of the PDE. For a second order differential equation we have three possible types of boundary conditions: (1) Dirichlet boundary condition, (2) von Neumann boundary conditions and (3) Mixed (Robin’s) boundary conditions.