From: Kevin Olbrich <redmine@...>
Date: 2010-07-13T12:25:54+09:00
Subject: [ruby-core:31234] [Bug #3563] problems with exponentiation, cbrt

Bug #3563: problems with exponentiation, cbrt
http://redmine.ruby-lang.org/issues/show/3563

Author: Kevin Olbrich
Status: Open, Priority: Normal
ruby -v: ruby 1.9.2dev (2010-07-02 revision 28524) [i386-darwin9.8.0]

# nothing required

> (-27)**(Rational(1,3)) #=> (1.5000000000000004+2.598076211353316i)

I would expect that this would return -3

> Complex(1.5000000000000004,2.598076211353316)**3 #=> (-27.000000000000007+1.2434497875801753e-14i)

I can understand how this might happen given round off errors, but the following identity should be true

Math.cbrt(-27) == (-27)**(Rational(1,3))  #=> false

Also note that if you do this...

> require 'complex'
> Math.cbrt(-27) #=> (1.5000000000000004+2.598076211353316i)


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