将系数矩阵分为四个部分，用光源可行区对行进行划分，用已知的表面节点对列进行划分,将方程转化为C*S=b-The coefficient matrix is ​ ​ divided into four parts, with the possible area of ​ ​ the light source row is divided by a known surface node column divided into the equation C* S