The distinction between covariance and contravariance is important for computations with tensors, which often have mixed variance.

协变和逆变的区别对于张量的计算尤为重要，这往往会出现混合方差。

Another concept that's very basic here is covariance.

另一个基本的概念是协方差。

Covariance is a measure of how much two variables move together.

协方差衡量的是两个变量一起变动的情况。

A negative covariance means that they tend to move opposite each other.

负值的协方差就表示，二者反向变动。

Significance and application of covariance functions are discussed.

对协方差函数的意义和应用做了讨论。