public static double Psi(
double x
)Public Shared Function Psi (
x As Double
) As Doublepublic:
static double Psi(
double x
)static member Psi :
x : float -> float The psi function, also called the digamma function, is the logrithmic derivative of the Γ function.

Because it is defined as a logarithmic derivative, the digamma function does not overflow Double even for arguments for which Gamma(Double) does.
To evaluate the psi function for complex arguments, use Psi(Complex).