Digamma Function/Examples/Digamma Function of Two

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Example of Use of Recurrence Relation for Digamma Function

$\map \psi 2 = -\gamma + 1$


Proof

\(\ds \map \psi {z + 1}\) \(=\) \(\ds \map \psi z + \frac 1 z\) Recurrence Relation for Digamma Function
\(\ds \leadsto \ \ \) \(\ds \map \psi {1 + 1}\) \(=\) \(\ds \map \psi 1 + 1\) $z := 1$
\(\ds \leadsto \ \ \) \(\ds \map \psi 2\) \(=\) \(\ds -\gamma + 1\) Digamma Function of One

$\blacksquare$