From: Axel Etzold <AEtzold@...>
Date: 2008-07-08T18:15:54+09:00
Subject: Re: Floating point calculation problem


-------- Original-Nachricht --------
> Datum: Tue, 8 Jul 2008 17:39:50 +0900
> Von: Hyun chul Park <paxcholy@gmail.com>
> An: ruby-talk@ruby-lang.org
> Betreff: Floating point calculation problem

Hi --

> hi.
> i'm confused by float point calculation.
> like this!
> 
> ------------------------------------------
> irb(main):001:0> 123.6 - 123
> => 0.599999999999994
> 
> ------------------------------------------
> 
> how to i get result 0.6 ?

you may want to take a look at this:

http://docs.sun.com/source/806-3568/ncg_goldberg.html

If you want to do exact calculations, you can use fractions

http://www.ruby-doc.org/stdlib/libdoc/rational/rdoc/classes/Rational.html

To convert between the two, for each real number (Float), you can use its continued fraction
approximation.

http://www.math.mtu.edu/mathlab/COURSES/holt/dnt/pell1.html

Here's a link to a Ruby program that calculates digits of Pi from its continued fraction representation
(and also a Java one, which is much longer):

http://www.cs.utsa.edu/~wagner/pi/pi_cont.html

Best regards,

Axel 

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