说明：  有限差分中的CN格式求解拉普拉斯方程。其中主要的THTA格式分成0-1之间100个数，用来验证其格式的收敛要求。
(CN finite difference scheme for solving the Laplace equation. One of the major THTA format into 100 number between 0 and 1, is used to verify the convergence requirements for the format.)