Services & Resources / Wolfram Forums / MathGroup Archive

MathGroup Archive 2013

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: Low precision exponentiation

  • To: mathgroup at
  • Subject: [mg129838] Re: Low precision exponentiation
  • From: awnl <awnl at>
  • Date: Mon, 18 Feb 2013 06:00:03 -0500 (EST)
  • Delivered-to:
  • Delivered-to:
  • Delivered-to:
  • Delivered-to:
  • References: <kfq6mm$4v5$>


> 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.

There are two problems here:

1) with the standard settings, Mathematica will print only 6 digits of 
machine precision numbers. You can change that in the preferences tab or 
with e.g.:

NumberForm[2.5^125, {16, 16}]

2) the input you are giving is interpreted to be machine precision in 
the first place. You can get an exact result like this:


and a numeric result to the desired precision like this:


alternatively you can define the precision with this syntax:


> I am inexperienced at Mathematica. Am I doing something silly?

yes and no, Mathematica handles arbitrary precision numbers in a 
somewhat unusual way. You might want to read the tutorials that are 
linked to the documentation of N to learn about some details. On the 
other hand, I think usually you can get away with the rule that one 
should try to stay with exact results as long as possible when 
requesting more than machine precision...



  • Prev by Date: Re: Mathematica and Lisp
  • Next by Date: Re: Low precision exponentiation
  • Previous by thread: Re: Low precision exponentiation
  • Next by thread: Re: Low precision exponentiation