说明：  本例用五点差分法求解一个二阶偏微分方程，其间用SSOR预处理的CG法处理，此实验可分别选取N=4，8，16，32
(This example uses a five-point difference method for solving second order partial differential equations, during which the CG with SSOR pre-treatment, were selected for this experiment can be N = 4,8,16,32)