把 Maxwell 方程式在时间和空间领域上进行差分化。利用蛙跳式(Leap frog algorithm)--空间领域内的电场和磁场进行交替计算，通过时间领域上更新来模仿电磁场的变化，达到数值计算的目的。-The Maxwell equations in time and space on the field differencing. Using the leapfrog (Leap frog algorithm)- Space field for alternating electric and magnetic fields calculated by the time domain electromagnetic field is updated to mimic the changes to achieve the purpose of numerical calculation.