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MathGroup Archive 1998

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Re: warning for Round[Log[2]/Log[4]]

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13940] Re: warning for Round[Log[2]/Log[4]]
  • From: bruck at math.usc.edu (Ronald Bruck)
  • Date: Tue, 8 Sep 1998 02:52:36 -0400
  • Organization: University of Southern California, Los Angeles, CA
  • References: <6ssvo6$m9r@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <6ssvo6$m9r at smc.vnet.net>,
Wouter Meeussen  <eu000949 at pophost.eunet.be> wrote:
>** this is not a bug report ***
>  Windows 3.0.0.0.  
>
[That Mathematica didn't have enough precision to compute Round[Log[2]/Log[4]]

Hmmm.  Interesting.  Since Log[2]/Log[4] = 1/2, Mathematica can't decide
whether to round up or down--it SHOULD apply round-to-even, to give
zero, but it's trying to do this with just numerical values.

As I recall, deciding when A == B is a profoundly difficult problem. 
I'm not sure how else one could go about this.  (Oh, sure, the
immediate problem could be fixed by applying a special rule for
logarithms, but what about special functions for which the relations
are still undiscovered?)

--Ron Bruck


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