In a nonlinear situation the matrices in the global matrix equation (Equation 3.22) derived in Chapter 3 are implicit functions of the unknown electromagnetic field. Because the nonlinear term is small and the matrices are sparse, these nonlinear algebraic equations can be solved more efficiently as essentially linear equations by using a simple nonlinear iteration scheme to account for the nonlinearity than as nonlinear equations requiring Newton-like methods [141]-[143].