但是，减法运算符是不可交换的；所以，需要两个操作来处理减数和被减数。
The subtract operator, however, is not commutative; therefore, you need two operations to handle the value to be subtracted and the value from which the subtraction will take place.
对于数学家来说，不可交换的对象与可交换的对象是一样真实的。
Noncommuting objects are as real to the mathematicians as commuting objects.
当你在组合这些操作的时候，矩阵的运算顺序是不可交换的，不同相乘顺序会导致不同的变换效果，这点很重要。
When you combine these operations, the results are not commutative - the order in which you multiply matrices is important.
应用推荐