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Re: New user question

• To: mathgroup at smc.vnet.net
• Subject: [mg20400] Re: New user question
• From: "Allan Hayes" <hay at haystack.demon.co.uk>
• Date: Tue, 26 Oct 1999 00:32:53 -0400
• References: <7uefh0$277@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

Thomas Moriarty <moriarty at umd5.umd.edu> wrote in message
news:7uefh0$277 at smc.vnet.net...
> 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?
>
> Thanks
>
>

Thomas,
You are not doing anything wrong - its that in the complex numbers, which is
what Mathematica uses, we have

(-1)^(1/3) // ComplexExpand

        1/2 + (I*Sqrt[3])/2

You might like to look at the standard add on package
Miscellaneous`RealOnly`


--
Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565