矩阵标准API（实矩阵相乘，Bsdet求实方阵的行列式值，求实方阵的逆）的C++封装，一个可复用的C++ 3阶方阵类和4阶方阵类-The a the matrix standard API (real matrix multiplication, Bsdet realistic matrix determinant value, realistic matrix inverse) C++ package, a reusable C++ 3 square matrix classes and 4