From: Jeremy Bopp <jeremy@...>
Date: 2011-05-12T05:06:40+09:00
Subject: Re: Math cube root

On 5/11/2011 14:45, Sergey Avseyev wrote:
> How can you explain this:
> 
>     $ irb
>     1.9.2p180 (main):001:0> 1000 ** (1.0/3)
>     9.999999999999998
>     1.9.2p180 (main):002:0> Math.sqrt(100)
>     10.0

You're using floating point arithmetic which is always inexact.  The
1.0/3 part cannot be represented with infinite precision, so it's
basically rounded at a certain point.  The result is then used for the
rest of the operation, which may compound the inaccuracy introduced by
the initial rounding.

If you must use floating point operations, be prepared to accept results
that are only *close* to what you expect, where close is largely
dependent on the operations being performed.

http://en.wikipedia.org/wiki/Floating_point

-Jeremy