来自《耶鲁大学开放课程：金融市场 第2集 第2集》

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  and it's the same idea except that--
  两个公式的思想是一样的
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  I'll also call it μx, except that it's an integral.
  都可以用μx表示 不过是一个积分
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  We have the integral from minus infinity
  积分下限是负无穷
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  to plus infinity of F*x*dx,
  上限是正无穷 然后对f(x)*x积分
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  and that's really--you see it's the same thing
  其实这两个式子是一样的
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  because an integral is analogous to a summation.
  因为积分也就是另一种形式的求和
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  Those are the two population definitions.
  这是两种对总体的定义
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  F(x) is the continuous probability distribution for x.
  F(x)是x的连续型随机变量的概率分布
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  That's different when you have continuous values--
  和离散型随机变量的分布不同的是
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  you don't have P(x = xi)
  连续型随机变量的分布中
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  because it's always zero.
  某一点的概率值始终是零
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  The probability that the temperature is exactly 100°
  温度恰好是整100摄氏度的概率是零