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MathGroup Archive 1999

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Re: New user question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg20405] Re: [mg20383] New user question
  • From: "David Park" <djmp at earthlink.net>
  • Date: Tue, 26 Oct 1999 00:32:56 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Thomas,

There are three values of the cube root of x, and for negative values Mathematica
picked one of the imaginary values. You can avoid this, and force Mathematica to
always pick the real solution by reading in the following package:

<<Miscellaneous`RealOnly`

Then your plot will work as expected. As an alternative solution you could use:

Plot[If[x < 0, -(-x)^(1/3), x^(1/3)], {x, -5, 5}];

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

>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
>
>
>



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