From owner-help-octave at bevo dot che dot wisc dot edu  Tue Nov 12 12:41:54 1996
Subject: fractional powers
From: Heber Farnsworth <heberf at u dot washington dot edu>
To: help-octave at bevo dot che dot wisc dot edu
Date: Tue, 12 Nov 1996 10:41:48 -0800 (PST)


I'm somewhat disturbed by the following behaviour on octave.  Perhaps it
is standard and I shouldn't be worried but it surprised me.  Consider the
following question: what is the cube root of -1?  Clearly the answer
should be -1.  Now ask octave

octave:1> x = (-1)^(1/3)
x = 0.50000 + 0.86603i

it gets wierder if you now cube that number

octave:2> x^3
ans = -1.0000e+00 + 1.2246e-16i
 
This is pretty close to the truth but still strange to my way of thinking.
Similar wierdness shows up with other fractional powers: 1/5, 1/7, etc.

Any thoughts?

  Heber Farnsworth                               | Department of Finance
  Univerity of Washington                        | Box 353200
  tele:  (206) 528-0793 home                     | Seattle, WA 98195-3200
  tele:  (206) 543-4773 finance     web: http://weber.u.washington.edu/~heberf
  fax:   (206) 685-9392             email: heberf at u dot washington dot edu