 The method shares many similarities to the finite-difference time-domain (FDTD) method, so much of the literature on FDTD can be directly applied.The method works by transforming Maxwell's equations (or other partial differential equation) for sources and fields at a constant frequency into matrix form formula_1.The matrix "A" is derived from the wave equation operator, the column vector "x" contains the field components, and the column vector "b" describes the source.