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Re: Low precision exponentiation

  • To: mathgroup at smc.vnet.net
  • Subject: [mg129851] Re: Low precision exponentiation
  • From: Helen Read <readhpr at gmail.com>
  • Date: Mon, 18 Feb 2013 06:04:23 -0500 (EST)
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  • References: <kfq6mm$4v5$1@smc.vnet.net>

The problem is that you entered 2.5 as a machine precision number, so 
you are only going to get machine precision output. The way to get high 
precision output is to start with the exact 5/2 instead of the machine 
precision 2.5.

N[(5/2)^125, 50]

In general, you should enter numbers into Mathematica exactly whenever 
possible. Enter rational numbers as fractions, and don't use decimal 
approximations for numbers like Pi or Sqrt[3]. Just put them in exactly, 
and then you can use N[] to get the output to whatever precision you want.

Helen Read
University of Vermont

On 2/17/2013 4:08 AM, Blaise F Egan wrote:
> I am trying to evaluate 2.5^125 to high precision.
>
> R gives 5.527147875260445183346e+49 as the answer but Mathematica
> with  N[2.5^125,30] gives 5.52715*10^49 and says that is to machine precision.>
> I am inexperienced at Mathematica. Am I doing something silly?
>
> Blaise
>






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