expected value

名词 expected value:

1. the sum of the values of a random variable divided by the number of values
   同义词：arithmetic mean, first moment, expectation

1. 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