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MathGroup Archive 2001

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Re: combining Log[] terms

  • To: mathgroup at smc.vnet.net
  • Subject: [mg30500] Re: combining Log[] terms
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Fri, 24 Aug 2001 04:05:59 -0400 (EDT)
  • References: <9m281v$h28$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Nicolas

The result is not valid in general

Log[1]-Log[-1]

        (-I)*Pi

Log[1/-1]

        I*Pi

But it does hold when a and b are both positive, and we have:

Simplify[Log[a] - Log[b], a>0&&b>0]

        Log[a/b]
--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Nicolas Bock" <nbock at acsu.buffalo.edu> wrote in message
news:9m281v$h28$1 at smc.vnet.net...
> 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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