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MathGroup Archive 2001

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Re: combining Log[] terms

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30492] Re: combining Log[] terms
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Fri, 24 Aug 2001 04:05:52 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <9m281v$h28$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

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 >
0]
Out[]=Log[a/b]

Regards
  Jens


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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