- Ursell function
In statistical mechanics, an Ursell function or connected correlation function, is a cumulant of a random variable. It is also called a connected correlation function as it can often be obtained by summing over connected Feynman diagrams (the sum over all Feynman diagrams gives the correlation functions).
(where E is the expectation).
The function was named after Harold Ursell, who introduced it in 1927.
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