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Topic: Low precision exponentiation
Replies: 5   Last Post: Feb 18, 2013 6:00 AM

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Helen Read

Posts: 145
Registered: 9/27/10
Re: Low precision exponentiation
Posted: Feb 18, 2013 6:00 AM
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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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