From: jzakiya <jzakiya@...>
Date: 2009-12-19T00:55:05+09:00
Subject: Re: Math errors

On Dec 18, 4:52 am, "Dasson, Raghav" <raghav.das...@sap.com> wrote:
> jzakiya wrote:
> > (-3)**3 => -27
>
> > (-27)**(1/3.0)  give NaN instead of -3
>
> > All odd roots (1/3,1/5,1/7 etc) of negative numbers should give
> > negative root values, as above, but ruby (in irb) gives NaN (not a
> > number), even when I require 'complex' .
>
> > Is this considered an error in Ruby?
>
> I guess, you are right. THIS IS A 'MATH ERROR' in Ruby.
>
> The ** method is not able to handle negative numbers raised to Floating points (that are not Integers)  

This behavior was shown in ruby ree 1.8.6, 1.8.6, 1.8.7, 1.9.1

-27**1/3.0       => -9.0
-27 ** 1/3.0     => -9.0
-27 ** (1/3.0)   => -3.0
-27**(1/3.0)     => -3.0
(-27)**(1/3.0)   => NaN
(-27) ** (1/3.0) => NaN

OK, the first two expression are evaluated as (-27**1)/3 => -9
The second two are correct (what I expected).
But the last two, WHY??