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A Greek psi of a variable, the gamma function's logarithmic derivative.
Also known as: Digamma function, Digamma psi, Polygamma of order zero
The digamma function is the derivative of the logarithm of the gamma function, and it is the tool for summing series of reciprocals in closed form. Its name is misleading: it has nothing to do with the archaic Greek letter digamma.
Denotes the logarithmic derivative of the gamma function.
Contexts: Mathematics
Sums finite series of reciprocals in closed form, which is its principal working use.
Contexts: Mathematics
Is written with a Greek psi and is unrelated to the archaic letter digamma its name suggests.
Contexts: Mathematics
A Greek lowercase psi — a curved cup on a vertical stroke that extends below the line — followed by a bracketed variable.