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Re: New user question

  • To: mathgroup at
  • Subject: [mg20393] Re: New user question
  • From: Harald Giese <giese at>
  • Date: Tue, 26 Oct 1999 00:32:49 -0400
  • Organization: Institut fuer Meereskunde, Universitaet Hamburg
  • References: <7uefh0$>
  • Sender: owner-wri-mathgroup at

Thomas Moriarty wrote:
> I have just begun to use/learn Mathematica.  One of the first things I
> tried was to Plot[x^(1/3),{x,-5,5}] and got error messages indicating that
> the negatives^(1/3) were not machine level real numbers (or close to
> that) - the positive side displayed ok.
> What am I doing wrong?

Hi Thomas,

Mathematica plots only real numbers, but the roots of negative reals are
complex numbers. Plot[Im[x^(1/3)], {x,-5,5}] will give you the imaginary
part, Plot[Abs[x^(1/3)], {x,-5,5}] the absolute values.

Every time Mathematica does not plot the result you expected, you should
first take a look at some of values you want to have plotted.


Harald Giese
Email: giese at
Phone: +49 (0)40 42838 5796; Fax: +49 (0)40 5605724
Institut fuer Meereskunde der Universitaet Hamburg
(Institute of Oceanography of the University of Hamburg)
Troplowitzstrasse 7, D-22529 Hamburg

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