From: Christopher Dicely <cmdicely@...>
Date: 2011-08-14T09:56:02+09:00
Subject: Re: Why this?

On Sat, Aug 13, 2011 at 12:28 PM, Николай <Godsent@mail.ru> wrote:
>
>
> -------- Original Message --------
> Subject:        Why this?
> Date:   Sat, 13 Aug 2011 22:20:04 +0300
> From:   Николай <godsent@tut.by>
> To:     ruby-talk@ruby-lang.org
>
>
>
> Hallow, can anybody explain me that?
> a = (10**2 + 5**2)                  #=>  125
> b = Math.hypot(10, 5)**2        #=>  125.0
> a == b                                     #=>false
> a.to_f == b                              #=>  false
> 125.0 == 125                          #=>  true
> 125.0.to_f == 125                   #=>  true

The second result is the version of "inspect" bundled with your ruby
installation misleading you.

Ruby 1.9.2p180, via RubyInstaller, Win7 32-bit gives me:

irb(main):001:0> a=(10**2 + 5**2)
=> 125
irb(main):002:0> b=Math.hypot(10,5)**2
=> 125.00000000000001

IronRuby 1.1 gives me behavior that looks like what you see, but a
quick test shows that that "125.0" inspect value is skin deep:

irb(main):001:0>  b=Math.hypot(10,5)**2
=> 125.0
irb(main):002:0> b<=>125.0
=> 1
irb(main):003:0> b==125.00000000000001
=> true

More generally, you are generally in deep trouble when you count on
floating point calculations producing exact results.