说明：  矩阵乘法是线性代数中最常见的运算之一，它在数值计算中有广泛的应用。若A和B是2个n×n的矩阵，则它们的乘积C=AB同样是一个n×n的矩阵
(Matrix multiplication is linear algebra is the most common operation, it is one of the numerical calculation is widely used. If A and B is 2 n* n matrix, then their product C = AB is also A n* n matrix )