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MathGroup Archive 2004

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Re: Log[4]==2*Log[2]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50635] Re: Log[4]==2*Log[2]
  • From: p-valko at tamu.edu (Peter Valko)
  • Date: Wed, 15 Sep 2004 01:49:34 -0400 (EDT)
  • References: <chp8q9$jjm$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Andreas,

In my view two symbolic expressions are not necessarily equal if
numerically they are equal.

What you wish to know is if the left and right hand sides can be
brought to a standard form and then if the standard forms are equal.
To achieve this you may wright:

(Log[4] // Simplify) == (2*Log[2] // Simplify)

that gives a solid True.


Regards
Peter





Andreas Stahel <sha at hta-bi.bfh.ch> wrote in message news:<chp8q9$jjm$1 at smc.vnet.net>...
> To whom it may concern
> 
> the following answer of Mathematica 5.0 puzzeled me
> 
> Log[4]==2*Log[2]
> leads to
> 
> N::meprec: Internal precision limit $MaxExtraPrecision = 50.` reached while \
> evaluating -2\Log[2]+Log[4]
> 
> with the inputs given as answer. But the input
> 
> Log[4.0]==2*Log[2]
> 
> leads to a sound "True"
> 
> Simplify[Log[4]-2*Log[2]]
> leads to the correct 0, but
> Simplify[Log[4]-2*Log[2]==0]
> yields no result
> 
> There must be some systematic behind thid surprising behaviour.
> Could somebody give me a hint please
> 
> With best regards
> 
> Andreas


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