Only center and neighboring points are used in present scheme , so the method of forward elimination and backward substitution can be directly used to solve linear simultaneous equations obtained from the scheme 该方法仅涉及中心点及相邻网格点,具有四阶精度,并且由所提格式得到的线性方程组是三对角线型的,可以直接采用追赶法进行求解。