说明：  passion方程的第一类边界条件的数值解，边界条件过于复杂而无法求得解析解。这就需要借助于数值法来求电磁场的数值解。有限差分法便是一种比较容易的数值解法。
(Numerical Solution of the first boundary condition passion equations and boundary conditions are too complex to be obtained by analytical solution. This requires the help of numerical methods to find numerical solution of electromagnetic fields. Finite difference method is a relatively easy numerical method.)