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6.8.17  Derivatives of the DiGamma function: Psi

The DiGamma function is the derivative of the logarithm of the Γ function (see Section 6.8.13),

ψ(z) =
d
dz
ln(Γ(z)) = 
Γ′(z)
Γ(z)
 

This function is used to evaluated sums of rational functions having poles at integers.

The Psi function computes the DiGamma function and its derivatives.


Examples.


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