From: Peter Vandenabeele <peter@...>
Date: 2011-12-16T21:20:08+09:00
Subject: Re: Rounding error?

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On Fri, Dec 16, 2011 at 1:09 PM, Vimal R. <email2vimalraj@gmail.com> wrote:

> Hi,
>
> I don't face this problem.
>
> When I follow the same code in my machine, I get proper result for
> 4.9 x 5.9 = 28.91
> 3.9 x 3.9 = 15.21
>

You most probably _do_ face the problem, but don't see it because the
_presentation_ of the result masks the small remainder errors. And what's
worse, the result might be dependent on the position of the moon (sorry,
joke, but the result will differ, based on the exact Ruby version, CPU
etc. that is used when the code is ran).

On ruby 1.9.3

peterv@e6500:~$ irb
ruby-1.9.3-p0 :001 > 4.9 * 5.9
 => 28.910000000000004
ruby-1.9.3-p0 :002 > "%35.30f"%(4.9 * 5.9)
 => "  28.910000000000003694822225952521"


On ruby 1.8.7

peterv@e6500:~$ rvm use 1.8.7-p330
Using /home/peterv/.rvm/gems/ruby-1.8.7-p330
peterv@e6500:~$ irb
no such file to load -- wirble
ruby-1.8.7-p330 :001 > 4.9 * 5.9
 => 28.91
ruby-1.8.7-p330 :002 > "%35.30f"%(4.9 * 5.9)
 => "  28.910000000000003694822225952521"

HTH,

Peter

-- 
Peter Vandenabeele
http://twitter.com/peter_v
http://rails.vandenabeele.com

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