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MathGroup Archive 1999

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Re: Simplify Log[ab] - Log[b] to Log[a] ?

  • To: mathgroup at
  • Subject: [mg16058] Re: Simplify Log[ab] - Log[b] to Log[a] ?
  • From: Paul Abbott <paul at>
  • Date: Tue, 23 Feb 1999 03:45:17 -0500
  • Organization: University of Western Australia
  • References: <7ao3po$>
  • Sender: owner-wri-mathgroup at

Simon Allfrey wrote:
> How do I persuade Mathematica to simplify
> Log[a b] - Log[b] to Log[a]?
> when processing algebraic expressions?

Use PowerExpand:

In[1]:= Log[a b] - Log[b]//PowerExpand
Out[1]= Log[a]

As another example,

In[2]:= Log[a b/c] - Log[b]//PowerExpand
Out[2]= Log[a] - Log[c]


Paul Abbott                                   Phone: +61-8-9380-2734
Department of Physics                           Fax: +61-8-9380-1014
The University of Western Australia           
Nedlands WA  6907                     mailto:paul at 

            God IS a weakly left-handed dice player

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