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Re: Bug? in PolyLog

  • To: mathgroup at
  • Subject: [mg21030] Re: [mg20925] Bug? in PolyLog
  • From: "Mark Harder" <harderm at>
  • Date: Thu, 2 Dec 1999 21:41:39 -0500 (EST)
  • Sender: owner-wri-mathgroup at

    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

-----Original Message-----
From: Francois Grieu <fgrieu at>
To: mathgroup at
Subject: [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

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