The variance of a random variable measures how far from the expected value its values typically are.
随机变量的方差衡量随机变量值与期望值偏离的程度。
The expected value of a positive integral power of a random variable. The first moment is the mean of the distribution.
矩，动差任意变量的正整数功效的期望值。第一个矩是分配的平均数。
The expected value of a positive integral power of a random variable. The first moment is the mean of the distribution.
矩，动差任意变量的正整数功效的期望值。第一个矩是分配的平均数。
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