2.4 Rules for Matrix Operations – 矩阵运算规则 一个矩阵如果有m行n列,那它就是一个m×nm\times nm×n矩阵 当两个矩阵形状相同的时候,就能够被相加。矩阵也能够被任意常数c所乘 [123400]+[224499]=[347899] and 2[123400]=[246800] \left[\begin{array}{ll} {1} & {2} \\ {3} & {4} \\ {0} & {0} \end{array}\right]+\left[\begin{array}{ll} {2} & {2} \\ {4} & {4} \\ {9} & {9}