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MathGroup Archive 1998

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg13950] Re: [mg13940] Re: warning for Round[Log[2]/Log[4]]
  • From: "George E. Hrabovsky" <georgeh at hep.physics.wisc.edu>
  • Date: Fri, 11 Sep 1998 15:06:40 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

When I do Log[2]/Log[4]//N I get 0.5, when I do Log[2]/Log[4]//N//Round
I get 0.

	George

----------
> From: Ronald Bruck <bruck at math.usc.edu>
To: mathgroup at smc.vnet.net
> To: mathgroup at smc.vnet.net
> Subject: [mg13950] [mg13940] Re: warning for Round[Log[2]/Log[4]]
> Date: Tuesday, September 08, 1998 1:52 AM
> 
> 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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