这是用vc编的LU分解法，也叫杜利 特儿法，子过程LUDCMP将矩阵分解 为上三角和下三角矩阵，子过程LU BKSB利用LUDCMP的分解结果得到线 性方程组的解-vc addendum to the LU decomposition method, also called Dulite abuse, LUDCMP sub-process decomposition of the matrix on the Triangle and lower trian