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C++ API

: psi (z)

: psi (k, z)

Compute the psi (polygamma) function.

The polygamma functions are the kth derivative of the logarithm of the gamma function. If unspecified, k defaults to zero. A value of zero computes the digamma function, a value of 1, the trigamma function, and so on.

The digamma function is defined:

psi (z) = d (log (gamma (z))) / dx

When computing the digamma function (when k equals zero), z can have any value real or complex value. However, for polygamma functions (k higher than 0), z must be real and non-negative.

See also: gamma, gammainc, gammaln.

Package: octave