The expectation value of a function in a variable is denoted or . For a single discrete variable, it is defined by
(1)
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where is the probability density function.
For a single continuous variable it is defined by,
(2)
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The expectation value satisfies
(3)
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(4)
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(5)
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For multiple discrete variables
(6)
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For multiple continuous variables
(7)
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The (multiple) expectation value satisfies
(8)
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(9)
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(10)
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where is the mean for the variable .