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Bug with ComplexExpand on PolyGamma?

• To: mathgroup at smc.vnet.net
• Subject: [mg15148] Bug with ComplexExpand on PolyGamma?
• From: Dirk Reiss <reiss at wserver.physnet.uni-hamburg.de>
• Date: Wed, 16 Dec 1998 03:11:22 -0500
• Sender: owner-wri-mathgroup at wolfram.com

Hallo,

when I apply 

In[1]:= ComplexExpand[Im[PolyGamma[a + I b]]]

I get the result:

Out[1]= 0

which is obviously not true. E.g. 

In[2]:= ComplexExpand[Im[PolyGamma[1 + I 3]]] //N

gives

Out[2]= 1.40413

is this a bug?


Greetings
Dirk Reiss

Institut fuer Laser-Physik
Universitaet Hamburg