Re: Re: Bug? in PolyLog
- To: mathgroup at smc.vnet.net
- Subject: [mg21048] Re: [mg21030] Re: [mg20925] Bug? in PolyLog
- From: Jeffry Baker <heavyb at surfree.com>
- Date: Sun, 12 Dec 1999 23:51:14 -0500 (EST)
- Sender: owner-wri-mathgroup at wolfram.com
Here is the results produced by version 2.2.2 on a Macintosh...
Regards,
JMB
In[1]:= (12/4/1999 at 12:35:19 AM)
PolyLog[2, 2.0]
Out[1]= (12/4/1999 at 12:35:19 AM)
2.4674 - 2.17759 I
In[2]:= (12/4/1999 at 12:35:34 AM)
Simplify[Im[PolyLog[2, 2]]]
Out[2]= (12/4/1999 at 12:35:34 AM)
2 2
-Pi (I Pi + Log[2]) 1
Im[---- - ---------------- - PolyLog[2, -]]
6 2 2
-------------------------------------------------------------------------
Francois,
Re. your input 1; I get the same result on vsn 3.0.1 running on
WindowsNT, Intel CPU. I don't understand why.
Re. input 2; This is because PolyLog[2,2] (exact arithmetic) does not
evaluate, but returns simply PolyLog[2,2], an expression with no Imaginary
part.
-mark
-----Original Message-----
From: Francois Grieu <fgrieu at micronet.fr>
To: mathgroup at smc.vnet.net
Subject: [mg21048] [mg21030] [mg20925] Bug? in PolyLog
>While trying to fix my Dickman function, I uncovered what appears
>to be a bug with the numerical implementation of PolyLog.
>It gives an imaginary part for PolyLog[2,x] for x>1
>when PolyLog[2,x] is purely real in this domain.
>
>Here is a session:
>
>Mathematica 4.0 Kernel for Power Macintosh
>Copyright 1988-1999 Wolfram Research, Inc.
> -- Terminal graphics initialized --
>
>In[1]:= PolyLog[2, 2.0]
>
>Out[1]= 2.4674 - 2.17759 I
>
>In[2]:= Simplify[Im[PolyLog[2, 2]]]
>
>Out[2]= 0
>
>
>Any clues ? I am interested by what happens for other releases
>of Mathematica.
>
> Francois Grieu
>