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Re: Working with Log

  • To: mathgroup at
  • Subject: [mg112118] Re: Working with Log
  • From: Simon <simonjtyler at>
  • Date: Tue, 31 Aug 2010 04:17:11 -0400 (EDT)
  • References: <i5g0ku$grr$>

Note that Log[a] + Log[b] does not always equal Log[a b], that being
Just write some replacement rules
logRep = x_. Log[a_] + y_. Log[b_] :> Log[a^x b^y]

Then, e.g.
In[2]:= y Log[2]+Log[x^2]-Log[z]
Out[2]= y Log[2]+Log[x^2]-Log[z]

In[3]:= %//.logRep
Out[3]= Log[(2^y x^2)/z]


On Aug 30, 8:20 pm, Themis Matsoukas <tmatsou... at> wrote:
> I can use PowerExapnd to expand a Log:
> PowerExpand[Log[a b]]
> Log[a] + Log[b]
> How can I do the opposite, i.e. combine Log[a] + Log[b] into Log[a b]?
> Thanks
> Themis

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