随机变量的方差衡量随机变量值与期望值偏离的程度。
The variance of a random variable measures how far from the expected value its values typically are.
随机变量的加权平均值是期望值。
The weighted mean of the random variable is the expected value.
3方差的专业定义是随机变量的二次中心矩，与期望值之差的平方的加权平均值。
The technical definition of variance is the random variable's second central moment, the weighted average of the square of the differences from the expected value.
本文讨论了系统的最优维修策略问题，考虑到题目中所涉及的变量大多为随机变量，我们建立了单目标的期望值模型。
Optimal maintenance policy problem in a system is discussed and analysed in this paper. Due to the random variable concerned, one objective mathematical model of expectation value is developed.
本文讨论了系统的最优维修策略问题，考虑到题目中所涉及的变量大多为随机变量，我们建立了单目标的期望值模型。
Optimal maintenance policy problem in a system is discussed and analysed in this paper. Due to the random variable concerned, one objective mathematical model of expectation value is developed.
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