说明：  自编数学函数调用库，有LU分解法，高斯塞德尔迭代法，追赶法解线性方程组，还有一维和二维的高斯积分公式
(writing mathematical function call library, LU decomposition, high Shisaideer iterative method, catching up with the method for solving linear equations, one-and two-dimensional Gaussian integral formula)