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MathGroup Archive 2001

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Re: combining Log[] terms

  • To: mathgroup at
  • Subject: [mg30492] Re: combining Log[] terms
  • From: Jens-Peer Kuska <kuska at>
  • Date: Fri, 24 Aug 2001 04:05:52 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <9m281v$h28$>
  • Sender: owner-wri-mathgroup at


because Log[a]-Log[b] == Log[a/b]
is only valid for a>0 and b>0. It 
is not correct for negative or complex
arguments. If you tell Mathematica
that a>0 and b>0 it will transform
the expression

In[]:=Simplify[Log[a] - Log[b], Element[{a, b}, Reals] && a > 0 && b >


Nicolas Bock wrote:
> Is there a function that combines terms like
> Log[a] - Log[b]
> to
> Log[a/b]?
> I couldn't find anything so far in the documentation regarding the
> Log[] function, only some references to Collect[], which does
> something similar to what I want for powers of a given expression.
>    Thanks already for you help,
>      nick

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