中文说明：二维FDTD正演模拟，PML二维吸收边界条件，增设PML阻抗渐变条件，波在传播过程中由阻抗渐变，传播路径及传播规律发生变化。模拟平面波在空间中的传播，最后结果以动画形式展现。
English Description：
Two dimensional FDTD forward simulation, PML two-dimensional absorption boundary conditions, add PML impedance gradient conditions, wave in the process of propagation by impedance gradient, propagation path and propagation law change. Simulation of plane wave propagation in space, the final results in the form of animation.