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Psi (digamma) Function
Syntax psi(X)
See Also exp , gamma , log , beta

Returns the element-by-element values for the psi function, where X is a real or double-precision matrix. The psi function is the logarithmic derivative of the gamma function.
               d      -
    psi(x)  =  -- ln | (x)
If x is negative, it is transformed to a positive argument by the reflection formula psi(1-x) = psi(x) + pi cot(pi x).

If you enter
O-Matrix will respond
which is Euler's constant.