From: Cameron McBride <cameron.mcbride@...>
Date: 2006-03-10T02:06:26+09:00
Subject: Re: ruby float calculations

On 3/9/06, Alexandru Toma <flash3001@yahoo.com> wrote:
> Could someone please explain to me why the following happens:
>
> irb(main):001:0> 0.29 - 0.38 + 0.1
> => 0.00999999999999998
> irb(main):002:0> 0.29 + (-0.38 + 0.1)
> => 0.00999999999999995
> irb(main):003:0> 0.29 + 0.1 - 0.38
> => 0.01

Check this out:

d1 = 0.29 - 0.38 + 0.1
d2 = 0.29 + (-0.38 + 0.1)
d3 = 0.29 + 0.1 - 0.38
p (d3 - d2)
p Float::EPSILON
(d3 - d2) < Float::EPSILON  #=> true

Computers do not store numbers indefinitely, so there is an "accuracy"
associated with floating point operations.   For more information,
check out:
  http://en.wikipedia.org/wiki/Floating_point

Cameron