中文说明：
利用有限差分法 (Finite Differential Method, FDM)将场域离散为许多小网格，应用差分原理，将求解连续函数的泊松方程问题转换为求解网格节点上的差分方程组的问题。
English Description：
The finite difference method (FDM) is used to discretize the field into many small grids. Using the difference principle, the problem of solving Poisson equation of continuous function is transformed into the problem of solving difference equations on grid nodes