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<B>PSI</B> _ _ _  _ _ _  _ _ _  _ _ _ <B>operator</B><P>
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The <em>Psi</em> operator returns the Psi (or DiGamma) function. 
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Psi(x) := df(Gamma(z),z)/ Gamma (z) 
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syntax: </H3>
<em>Gamma</em>(&lt;expression&gt;) 
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examples: </H3>
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Psi(3); 

  (2*log(2) + psi(1/2) + psi(1) + 3)/2 


on rounded; 

- Psi(1); 

  0.577215664902

</TT></PRE><P>Euler's constant can be found as - Psi(1). 
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