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Problems with PolyGamma

• To: mathgroup at smc.vnet.net
• Subject: [mg22151] Problems with PolyGamma
• From: abdo at euroseek.com (Abds Roig)
• Date: Wed, 16 Feb 2000 02:35:16 -0500 (EST)
• Organization: The Math Forum
• Sender: owner-wri-mathgroup at wolfram.com

Hello. My name is Abdó Roig and I'm from Spain (sorry if my english
isn't good).

I've Mathematica 2.2 and I've found a problem with PolyGamma function.
I was evaluating expressions like "PolyGamma[10^10]" and I found that
the output of this expression is "- EulerGamma - 2Log2". This result
is the same as the output of PolyGamma with integers near 10^10 or
greater. Always is the same. I think it's wrong. If I use
"N[PolyGamma[10^10]]" the output is -1.963......, the same.

Then I tried to evaluate N[PolyGamma[10^10+1/10]], where 1/10 should
not cause relevant changes on the result, but the output of this
expression is 23.0259... (which seems to be a "correct" output).

I think it's a bug of Mathematica. I would be very pleased if somebody
could give me more information about it.

Thanks.

--

Abdo Roig
abdo at euroseek.com