From: Gary Wright <gwtmp01@...>
Date: 2011-09-18T14:08:24+09:00
Subject: Re: Strange vector behaviour


On Sep 17, 2011, at 10:26 PM, thomas Mulvaney wrote:
> Vector[2,4,6] == Vector[1,2,3]*2
> #=> true
> 
> It returns true as expected.
> 
[...]
> Vector[1.1,2.2,3.3] == Vector[1,2,3]*1.1
> #=> false
> 
> Any ideas whats going on?

Integer literals have exact representations while floats do not.  Decimal floating point numbers in general can not be represented exactly in binary so there is a conversion from the string "1.1", for example, to the binary floating point number that is "closest" to 1.1:

>> "%0.60f" % 1.1 #=> "1.100000000000000088817841970012523233890533447265625000000000"

Of course this means that multiple of 1.1 aren't exactly what you might expect:

>> "%0.60f" % (1.1 * 3) #=> "3.300000000000000266453525910037569701671600341796875000000000"

Here is the obligatory reference for this topic:

<http://download.oracle.com/docs/cd/E19957-01/806-3568/ncg_goldberg.html>

Gary Wright