1、对求解区域进行网格剖分，网格越小，精度越高。
2、将边界条件离散到格点上。
3、用五点差分建立求解方程，求出各个各点上的函数值。(1, mesh the mesh of the solution, the smaller the grid, the higher the accuracy.　　　　　 2, the boundary conditions are discretized to the grid.　　　　　 3, five point difference is used to establish the equation, and find the function values at each point.)